Email sending system

Abstract

To provide an electronic mail transmission system which safely transmits an attached file and in which interruption of electronic mail does not occur.SOLUTION: When an attached file is attached to transmission mail, a transmission-side mail server 3 included in an electronic mail transmission system 2 confirms whether or not a destination-side mail server 7 is adapted to TLS communications. In a case where it is adapted to TLS, the transmission mail including the attached file is sent to the destination-side mail server 7 via an encrypted communication path which is encrypted by TLS. In a case where the destination-side mail server 7 is not adapted to TLS, on the other hand, the attached file separated from the transmission mail is sent toward an attached file storage server 4, and the attached file is provided from the attached file storage server 4 or the separated attached file is compressed into a compression file with a password, attached to the transmission mail again and sent to the destination-side mail server 7 via a non-encrypted communication path which is not encrypted by TLS.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electronic mail transmission system including a sending mail server that sends outgoing mail created on a sender's terminal to a destination mail server. [Background technology]

[0002] In previous email systems, the communication path between mail servers was not encrypted, and plaintext emails were sent. Since files attached to emails can contain highly confidential information, in an attempt to reduce the risk of attachments being intercepted, attachments are compressed into password-protected ZIP files and this ZIP file is then attached to the outgoing email. After sending an email with the ZIP encrypted file attached, the sender creates another email containing the password to unzip the ZIP encrypted file and sends it to the same recipient.

[0003] According to a survey conducted by the inventor, it has been confirmed that approximately 90% of communication paths between mail servers are encrypted today, using highly secure communication protocols such as TLS (Transport Layer Security).

[0004] Several e-mail systems have been proposed to date that utilize the fact that communication paths between mail servers are encrypted. For example, the e-mail server device described in Patent Document 1 below is known.

[0005] This email server device determines whether communication with the destination mail server is possible using a secure communication procedure such as SSL (Secure Socket Layer) or TLS, and if communication is possible, delivers the email using the secure communication procedure.On the other hand, if communication with the destination mail server using a secure procedure is not possible, the email is delivered as is or the delivery is stopped. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-345403 Summary of the Invention [Problem to be solved by the invention]

[0007] In the email server device described in Patent Document 1, if communication using a secure communication procedure is not possible, the email is delivered without using a secure communication procedure, which creates a risk of eavesdropping.Furthermore, if delivery is stopped when communication using a secure communication procedure is not possible, email communication is interrupted, which makes the device less user-friendly.

[0008] Because attachments often contain more confidential information than the main text of an email, there was a demand for an easy-to-use email transmission system that could send attachments safely and prevent email delivery interruptions.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an e-mail transmission system that can safely transmit attached files and that does not cause e-mail interruptions. [Means for solving the problem]

[0010] In order to solve the above problem, the invention described in claim 1 is an electronic mail transmission system including a sending mail server that sends outgoing mail created on a sender terminal to a destination mail server, wherein the sending mail server includes an outgoing mail acceptance unit that accepts the created outgoing mail from the sender terminal, an attachment detection unit that detects whether or not the accepted outgoing mail has an attachment, an encrypted communication compatibility information inquiry unit that acquires encrypted communication compatibility information from the destination mail server, the encrypted communication compatibility information including information whether or not the destination mail server of the outgoing mail supports encrypted communication, an attachment separation unit that separates the attachment from the outgoing mail and divides it into the attachment and the outgoing mail from which the attachment has been removed, and a message indicating the attachment when the destination mail server does not support encrypted communication. To safely sendand an encrypted communication determination process control unit that controls the sending of the outgoing mail based on the encrypted communication compatibility information acquired by the encrypted communication compatibility information inquiry unit, wherein when the attachment detection unit detects that the outgoing mail has the attached file, the encrypted communication determination process control unit causes the encrypted communication compatibility information inquiry unit to acquire the encrypted communication compatibility information of the destination mail server, and when it is confirmed from the acquired encrypted communication compatibility information that the destination mail server is compatible with the encrypted communication, causes the outgoing mail sending unit to select an encrypted communication path encrypted by the encrypted communication and send the outgoing mail including the attached file to the destination mail server, and when it is confirmed that the destination mail server is not compatible with the encrypted communication, causes the encrypted communication determination process control unit to The attachment separated from the outgoing email by the attachment separation unit is sent based on the settings of the outgoing email sending setting storage unit, and the outgoing email from which the attachment has been removed is sent to the outgoing email sending unit toward the destination mail server through an unencrypted communication path that is not encrypted by the encrypted communication, and the encrypted communication compatibility information includes the encryption version and cipher suite of the encrypted communication, and when it is determined that there is a high security risk based on the encryption version and the cipher included in the cipher suite, even if the destination mail server is compatible with the encrypted communication, the encrypted communication determination processing control unit determines that the destination mail server is not compatible with the encrypted communication and sends the attachment separated from the outgoing email by the attachment separation unit based on the settings of the outgoing email sending setting storage unit.

[0011] The invention of claim 2, in addition to the configuration of claim 1, further comprises an attachment storage server that stores the attachment and provides the stored attachment in response to a request for providing the attachment, the attachment storage server having an attachment reception unit that receives the attachment sent from the sending mail server, an attachment storage unit that stores the received attachment, an attachment provision request reception unit that receives the request for providing the attachment stored in the attachment storage unit, and an attachment provision unit that provides the attachment to a request source that sent the provision request, the sending mail server having an attachment upload unit that sends the attachment to the attachment storage server, the sending mail server further having a compression / decompression password generation unit that generates a compression / decompression password that is applied to encryption / compression conversion to compress the attachment into a password-protected compressed file and that is also applied to decryption / decompression conversion to decompress the password-protected compressed file into the attachment before compression, and and an attachment storage server configured to receive the attachment sent from the attachment upload unit, and store the received attachment in the attachment storage unit, and then, when the attachment provision request receiving unit receives the provision request for the attachment, the attachment provision unit provides the attachment to the request source that sent the provision request. The sending mail server is configured such that the attachment compression unit applies the compression / decompression password generated by the compression / decompression password generating unit to the attachment separated by the attachment separation unit to create the password-protected compressed file, and the compressed file re-attachment unit re-attaches the created password-protected compressed file to the outgoing mail from which the attachment has been removed. The aforementionedAfter reattaching it to an outgoing email, the password-protected compressed file is attached to the outgoing email. In front The outgoing mail sending unit sends the attachment to the destination mail server, and the sending method of the attachment set in the outgoing mail sending setting storage unit is set to be selectable between sending the attachment separated by the attachment separation unit from the attachment upload unit to the attachment storage server, or compressing the attachment separated by the attachment separation unit into the password-protected compressed file and sending the outgoing mail with the password-protected compressed file attached from the outgoing mail sending unit to the destination mail server.

[0012] The invention according to claim 3, in addition to the configuration of claim 2, is characterized in that the outgoing mail sending setting storage unit is also configured to pre-set a sending method for the outgoing mail from which the attachment has been removed, and when it is confirmed that the destination mail server does not support encrypted communication or when it is determined that the destination mail server does not support encrypted communication, the outgoing mail sending unit sends the outgoing mail from which the attachment has been removed by the attachment separation unit based on the setting of the outgoing mail sending setting storage unit, and the sending method for the outgoing mail from which the attachment has been removed, which is configured in the outgoing mail sending setting storage unit, is selectable from among: suspending the outgoing mail for a predetermined time and sending the outgoing mail after the predetermined time has elapsed; adding a predetermined email address to a blind carbon copy of the outgoing mail and then sending the outgoing mail; canceling the sending of the outgoing mail; sending the outgoing mail after approval by a predetermined approver; sending the outgoing mail and notifying a pre-registered email address; or immediately sending the outgoing mail. 。

[0013] Claim 4 The invention according to claim 2 toIn addition to the described configuration, the sending mail server has an outgoing mail body appending unit that appends text to the body of the outgoing mail, and the encrypted communication determination processing control unit controls the outgoing mail body appending unit to append text to the body of the outgoing mail indicating whether the destination mail server supports encrypted communication or not, based on the encrypted communication support information of the destination mail server obtained by the encrypted communication support information inquiry unit.

[0014] Claim 5 The invention according to claim 4 In addition to the configuration described above, the sending mail server has a sender terminal notification unit that notifies the sender terminal that sent the outgoing email, and the encrypted communication determination processing control unit controls the sender terminal notification unit to notify the sender terminal of whether or not the outgoing email has been sent to the destination mail server through the encrypted communication path.

[0015] Claim 6 The invention according to claim 5 In addition to the configuration described above, an administrator terminal that manages the email transmission status of the sender terminal is connected to the sending mail server so as to be able to communicate with the sending mail server, the sending mail server has an administrator terminal notification unit that notifies the administrator terminal of the transmission result of the outgoing mail sent from the sender terminal, and the encrypted communication determination processing control unit notifies the administrator terminal of the content indicating whether the outgoing mail has been sent to the destination mail server through the encrypted communication path. At the end The administrator terminal notification unit is controlled to notify the administrator terminal.

[0016] Claim 7 The invention according to claim 6In addition to the configuration described above, the sending mail server has a sent mail history memory unit that stores, for each sent mail sent from the sender terminal, sending history information including information on whether the sent mail has been sent to the destination mail server through the encrypted communication path, sender information, and destination information, a sent mail history report creation unit that creates a sent mail history report based on the sending history information of the multiple sent mails stored in the sent mail history memory unit, and a sent mail history report providing unit that provides the sent mail history report created by the sent mail history report creation unit, and the sent mail history report includes personal data that is the number of encrypted communication mails, which is the number of sent mails sent to the destination mail server through the encrypted communication path, the number of unencrypted communication mails, which is the number of sent mails sent through the unencrypted communication path, and the ratio of the number of encrypted communication mails and the number of unencrypted communication mails to the total number of sent mails, compiled for each sender and / or destination, or statistical information data that is the compilation of the personal data of multiple senders and / or multiple destinations.

[0017] Claim 8 The invention according to claim 4 In addition to the configuration described above, the sending mail server has a pseudo screen creation unit that creates a pseudo display screen in which the sending mail body appending unit adds text to the body of the sending mail, and a pseudo screen providing unit that provides a pseudo screen of the sending mail created by the pseudo screen creation unit, and is characterized in that it can create the pseudo screen of the sending mail when the destination mail server supports the encrypted communication and the sending mail is sent through the encrypted communication path, and the pseudo screen of the sending mail when the destination mail server does not support the encrypted communication and the sending mail is sent through the unencrypted communication path, regardless of the sending of the sending mail.

[0018] The invention of claim 9 is an electronic mail transmission system including a sending mail server that sends outgoing mail created on a sender terminal to a destination mail server, wherein the sending mail server includes a sending mail acceptance unit that accepts the created outgoing mail from the sender terminal, an encrypted communication compatibility information inquiry unit that acquires encrypted communication compatibility information from the destination mail server, including information on whether the destination mail server of the outgoing mail supports encrypted communication, an outgoing mail sending setting storage unit that stores in advance settings for a sending method of the outgoing mail when the destination mail server does not support encrypted communication, and a sending mail sending unit that sends the outgoing mail to the destination mail server. and an encrypted communication determination process control unit that controls the sending of the outgoing mail based on the encrypted communication compatibility information acquired by the encrypted communication compatibility information inquiry unit, wherein the encrypted communication determination process control unit causes the encrypted communication compatibility information inquiry unit to acquire the encrypted communication compatibility information of the destination mail server, and when it is confirmed from the acquired encrypted communication compatibility information that the destination mail server is compatible with the encrypted communication, causes the encrypted communication determination process control unit to select an encrypted communication path encrypted by the encrypted communication and send the outgoing mail to the outgoing mail sending unit toward the destination mail server, and when it is confirmed that the destination mail server is not compatible with the encrypted communication, If the outgoing email has an attachment, the attachment is encrypted and compressed into a password-protected compressed file and reattached to the outgoing email, and regardless of whether the outgoing email has an attachment, Based on the settings of the outgoing mail sending setting holding unit, the outgoing mail is sent to the outgoing mail sending unit through a non-encrypted communication path that is not encrypted by the encrypted communication, and the encrypted communication compatibility information includes the encryption version of the encrypted communication and the cipher suite of the encrypted communication, and when it is determined that there is a high security risk based on the encryption version and the cipher included in the cipher suite, even if the destination mail server is compatible with the encrypted communication, the encrypted communication determination processing control unit sends the outgoing mail based on the settings of the outgoing mail sending setting holding unit, assuming that the destination mail server is not compatible with the encrypted communication.

[0019] Claim 10The invention according to claim 9 In addition to the configuration described above, the sending method of the outgoing mail set in the outgoing mail sending setting holding unit is set to be selectable from among: holding the outgoing mail for a predetermined time and sending the outgoing mail after the predetermined time has elapsed; adding a predetermined email address to a blind carbon copy of the outgoing mail and then sending the outgoing mail; canceling the sending of the outgoing mail; sending the outgoing mail after approval by a predetermined approver; sending the outgoing mail and notifying a pre-registered email address; or sending the outgoing mail immediately. [Effects of the Invention]

[0020] Claim 1 of According to the invention, when it is confirmed that the destination mail server supports encrypted communication, an encrypted communication path encrypted by that encrypted communication is selected and the outgoing mail including the attachment is sent to the destination mail server, while when it is confirmed that the destination mail server does not support encrypted communication, the attachment is sent based on the setting of the outgoing mail sending setting storage unit and the outgoing mail without the attachment is sent to the destination mail server via an unencrypted communication path that is not encrypted by encrypted communication. In this way, an email sending system is realized which can send attachments safely and does not cause email delivery interruptions.

[0021] Claim 2According to the invention, when the destination mail server does not support encrypted communication, the method of sending an attachment is either to send the attachment to an attachment storage server and provide the attachment via the attachment storage server, or to compress the attachment into a password-protected compressed file, attach the password-protected compressed file to an outgoing email, and send it to the destination mail server. This allows the attachment to be sent safely. The sending method using an attachment storage server ensures a higher level of security. On the other hand, the method of attaching a password-protected compressed file to an outgoing email and sending it to the destination mail server eliminates the need to install an attachment storage server, simplifying the system configuration.

[0022] Also, claims 2 According to the invention, when the destination mail server does not support encrypted communication, the method of sending the attachment can be selected from either sending the attachment to an attachment storage server and providing the attachment via the attachment storage server, or compressing the attachment into a password-protected compressed file, attaching the password-protected compressed file to the outgoing mail, and sending it to the destination mail server. This makes it easy to set the method of sending the attachment, and realizes a system that is easy to introduce and easy to use.

[0023] Claim of 3 According to the invention, there are multiple methods for sending outgoing emails with attachments removed when the destination mail server does not support encrypted communication, and various settings are possible. In addition, settings can be flexibly realized according to the needs of the user.

[0024] Also, claims of 3According to the invention, the sending method for outgoing emails with attachments removed when the destination email server does not support encrypted communication can be selected from multiple options. This makes it easy to set the sending method, resulting in a system that is easy to implement and easy to use.

[0025] Claim 4 According to the invention, a sentence indicating whether the destination mail server supports encrypted communication or not is added to the body of the outgoing email, so when you receive the outgoing email, you can check whether the email was sent through an encrypted communication path that is encrypted by encrypted communication or not.

[0026] Claim 5 According to the invention, it is possible to check at the sender's terminal whether or not the outgoing mail has been sent through an encrypted communication path that has been encrypted by encrypted communication.

[0027] Claim 6 According to the invention, it is possible to check at the administrator terminal whether or not an outgoing email has been sent through an encrypted communication path.

[0028] Claim 7 According to the invention, by checking the created sent mail history report, it is possible to perform a detailed analysis of the history, such as how many sent mails were sent through the encrypted communication path.

[0029] Claim 8 According to the invention, the display screen of the outgoing mail to be delivered to the destination can be checked in advance.

[0030] According to the invention of claim 9, when it is confirmed that the destination mail server supports encrypted communication, the outgoing email is sent to the destination mail server by selecting an encrypted communication path encrypted by that encrypted communication. On the other hand, when it is confirmed that the destination mail server does not support encrypted communication, the outgoing email is sent to the destination mail server through an unencrypted communication path that is not encrypted by encrypted communication based on the settings of the outgoing email sending setting storage unit. As a result, when the destination mail server supports encrypted communication, the outgoing email is sent safely by encrypted communication, and when the destination mail server does not support encrypted communication, the outgoing email is sent using a predetermined sending method. This allows the sender or administrator of the outgoing email to know in advance the safety when the destination mail server does not support encrypted communication. Furthermore, an email sending system that does not cause email interruptions can be realized. On the other hand, if it is confirmed that the destination mail server does not support encrypted communication, if an attachment is attached to the outgoing mail, the attachment is encrypted and compressed into a password-protected compressed file and reattached to the outgoing mail, and regardless of whether an attachment is attached to the outgoing mail or not, the outgoing mail is sent to the outgoing mail sending section through an unencrypted communication path that is not encrypted by the encrypted communication based on the settings of the outgoing mail sending setting holding section, thereby realizing an email sending system that achieves both the secure sending of attachments and the prevention of email interruptions.

[0031] Claim 10 According to the invention, there are multiple methods for sending outgoing emails when the destination email server does not support encrypted communication, and various settings are possible. Also, settings can be flexibly realized according to the needs of users such as senders and administrators of outgoing emails.

[0032] Also, claims 10 According to the invention, when the destination mail server does not support encrypted communication, the sending method for outgoing mail can be selected from multiple options. This makes it easy to set the sending method, and realizes a system that is easy to introduce and use. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is a block diagram showing the configuration of an electronic mail system including an electronic mail transmission system in accordance with Embodiment 1 of the present invention. [Figure 2] 2 is a schematic functional block diagram of a sending mail server included in the email sending system according to the first embodiment. FIG. [Figure 3] 3 is a schematic diagram of an outgoing mail sending setting screen provided by the email sending system according to the first embodiment. FIG. [Figure 4] 1A and 1B are schematic diagrams showing examples of email display screens displayed to a recipient by an email sending system according to the first embodiment, in which (a) shows an email screen sent via an unencrypted communication path that is not encrypted by TLS communication, and (b) shows an email screen sent via an encrypted communication path that is encrypted by TLS communication. [Figure 5] 2 is a schematic functional block diagram of an attachment file storage server included in the email transmission system according to the first embodiment. FIG. [Figure 6] FIG. 1 is a schematic diagram showing the flow of sending an e-mail in an e-mail system including the e-mail sending system according to the first embodiment, and shows the flow of sending an attachment to an attachment storage server when the destination mail server does not support TLS. [Figure 7] FIG. 1 is a schematic diagram showing the flow of sending an e-mail in an e-mail system including the e-mail sending system according to the first embodiment. However, if the destination mail server does not support TLS, the attached file is compressed into a password-protected compressed file, and the compressed file is attached to the outgoing e-mail and sent to the destination mail server. [Figure 8] FIG. 10 is a block diagram showing the configuration of an electronic mail system including an electronic mail transmission system in accordance with a second embodiment of the present invention. [Figure 9] FIG. 10 is a schematic functional block diagram of a sending mail server included in the email sending system according to the second embodiment. [Figure 10] 10 is a schematic diagram showing the flow of sending an e-mail in an e-mail system including the e-mail sending system according to the second embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0034] [First embodiment of the invention] A first embodiment of the present invention will be described with reference to FIGS.

[0035] FIG. 1 is a block diagram showing a schematic configuration of an email system 1 including an email transmission system 2 according to a first embodiment of the present invention.

[0036] In this email system 1, a sending mail server 3, an attachment file storage server 4, and a destination mail server 7 are connected via a communication line 9 such as the Internet. A sender terminal 5, which sends outgoing emails created by the sender terminal 5, and an administrator terminal 6, which manages the email sending status of the sender terminal 5, are communicatively connected to the sending mail server 3. A destination terminal 8, which is the destination of the outgoing email, is communicatively connected to the destination mail server 7. The destination terminal 8 is also connected to the communication line 9, and is capable of downloading files stored in the attachment file storage server 4 via the communication line 9.

[0037] Server devices are used for the sending mail server 3, the attachment file storage server 4, and the destination mail server 7. Information terminals such as PCs (Personal Computers), smartphones, and tablets are used for the sender terminal 5, the administrator terminal 6, and the destination terminal 8, and each includes a CPU (Central Processing Unit), an auxiliary storage device which is a nonvolatile storage device, a control unit including RAM (Random Access Memory), a display unit, an input unit, etc. (not shown).

[0038] An e-mail transmission system 2 is configured to include a sending mail server 3 and an attachment file storage server 4 .

[0039] When a sending mail server 3 included in the email transmission system 2 accepts an outgoing mail created by a sender terminal 5, it sends the accepted outgoing mail to a destination mail server 7. The destination mail server 7 accepts and stores the outgoing mail, and provides the outgoing mail to the destination terminal 8 in response to a request from the destination terminal 8.

[0040] The sending mail server 3 detects whether an attachment is attached to the outgoing mail, and if it detects that an attachment is attached, it queries the destination mail server 7 of the outgoing mail to obtain encrypted communication support information, including whether the destination mail server 7 supports encrypted communication. The "encrypted communication" may be any encrypted communication protocol, such as SSL or TLS, but the following explanation will be given taking TLS as an example of "encrypted communication."

[0041] If it is confirmed from the acquired encrypted communication support information that the destination mail server 7 supports TLS communication, the outgoing mail including the attachment is sent from the sending mail server 3 to the destination mail server 7 through an encrypted communication path encrypted based on TLS. On the other hand, if it is confirmed that the destination mail server 7 does not support TLS communication, the attachment separated from the outgoing mail is sent by a sending method preset in the outgoing mail sending setting holding unit 304 of the sending mail server 3, and the outgoing mail with the attachment removed is sent to the destination mail server 7 through an unencrypted communication path that is not encrypted by TLS.

[0042] The methods of sending an attachment set in the outgoing mail sending setting holding unit 304 include sending the attachment to the attachment storage server 4 and providing the attachment via this attachment storage server 4, or encrypting and compressing the attachment into a password-protected compressed file, reattaching this password-protected compressed file to the outgoing mail, and sending it to the destination mail server 7 via an unencrypted communication path that is not encrypted by TLS. For example, a password-protected ZIP compressed file can be used as the password-protected compressed file.

[0043] In the sending method using the attachment storage server 4, the attachment sent from the sending mail server 3 is received by the attachment storage server 4 and the received attachment is stored. After that, when a request to provide the attachment is sent from the destination terminal 8 and received by the attachment storage server 4, the attachment storage server 4 provides the attachment to the destination terminal 8 that sent the request.

[0044] In the sending method for reattaching a password-protected compressed file to an outgoing email, first, a compression / decompression password is generated on the sending mail server 3, which is applied to the encryption / decompression conversion that compresses the attached file into a password-protected compressed file. This compression / decompression password is also applied to the decryption / decompression conversion that decompresses the password-protected compressed file back into the original attached file.

[0045] Next, the generated compression / decompression password is applied to the attachment separated from the outgoing email to create a password-protected compressed file, and this password-protected compressed file is reattached to the outgoing email from which the attachment was removed.Then, the outgoing email with the password-protected compressed file attached is sent to the destination mail server 7 via an unencrypted communication path that is not encrypted by TLS.

[0046] If the destination mail server 7 supports TLS communication, the sender mail server 3 can safely send the outgoing mail including the attachment to the destination mail server 7 via an encrypted communication path encrypted by TLS communication.

[0047] On the other hand, if the destination mail server 7 does not support TLS communication, the sender mail server 3 sends the attachment separated from the outgoing mail to the attachment storage server 4, and the attachment is provided securely from the attachment storage server 4. Alternatively, the attachment is encrypted into a password-protected compressed file and sent securely.

[0048] Attachments can be sent more securely by sending them to the attachment storage server 4 and providing them from this attachment storage server 4. On the other hand, the method of compressing the attachment into a password-protected compressed file and reattaching it to the outgoing email for sending does not require the installation of the attachment storage server 4, simplifying the system configuration.

[0049] Furthermore, even if the destination mail server 7 does not support TLS communication, the outgoing mail from which the attachment has been removed is sent to the destination mail server 7, so the e-mail will not be interrupted.

[0050] 2 is a schematic functional block diagram of the sending mail server 3. This sending mail server 3 is configured to include a control unit 30, an outgoing mail reception unit 32, a destination detection unit 34, an outgoing mail sending unit 36, a communication unit 38, and a TLS communication determination processing unit 300 as an "encrypted communication determination processing unit."

[0051] The control unit 30 is configured to include a CPU (not shown), an auxiliary storage device which is a nonvolatile storage device, and RAM. The CPU executes programs, performs arithmetic processing, and controls the elements that make up this sending mail server 3. The auxiliary storage device stores programs executed by the CPU, registration data, etc., and may be an HDD (Hard Disk Drive) or SSD (Solid State Drive). The RAM is used as a work area for the CPU to execute programs and perform arithmetic processing.

[0052] The outgoing mail reception unit 32 receives outgoing mail sent from the sender terminal 5 under the control of the control unit 30. This outgoing mail is created by the sender terminal 5. The destination detection unit 34 detects the destination of the outgoing mail received by the outgoing mail reception unit 32 under the control of the control unit 30.

[0053] The outgoing mail sending unit 36 ​​sends outgoing mail to the destination mail server 7. This outgoing mail sending unit 36 ​​can send outgoing mail by selecting an encrypted communication path encrypted by TLS, and can also send outgoing mail through an unencrypted communication path that is not encrypted by TLS.

[0054] The communication unit 38 transmits and receives data to and from the outside of the sending mail server 3 .

[0055] The TLS communication determination processing unit 300 includes an encrypted communication determination processing control unit 301, an outgoing mail sending setting screen providing unit 302, an outgoing mail sending setting accepting unit 303, an outgoing mail sending setting holding unit 304, an attachment detection unit 306, a TLS communication support information inquiry unit 308 as an "encrypted communication support information inquiry unit", a TLS communication support status determination unit 310 as an "encrypted communication support status determination unit", an attachment separation unit 312, a compression / decompression password generation unit 314, an attachment compression unit 316, an outgoing mail body appending unit 318, a compressed file re-attachment unit 320, a password-included email creation unit 321, a sender terminal notification unit 322, an administrator terminal notification unit 324, a download URL (Uniform Resource Locator) Locator generation unit 326, download password generation unit 328, attachment file upload unit 330, sent mail history storage unit 332, sent mail history providing unit 334, sent mail history report creation unit 336, sent mail history report providing unit 338, pseudo screen creation unit 340, and pseudo screen providing unit 342.

[0056] The TLS communication determination unit 300 detects whether an attachment is attached to an outgoing email. If an attachment is detected, the TLS communication determination unit 300 queries the destination mail server 7 of the outgoing email to obtain TLS communication support information, which is "encrypted communication support information" including information on whether the destination mail server 7 supports TLS. This TLS communication support information includes, in addition to information identifying whether the destination mail server 7 supports TLS, information such as the TLS encryption version, the TLS server certificate, the expiration date of the TLS server certificate, and the cipher suite. If the obtained TLS communication support information confirms that the destination mail server 7 supports TLS communication, the outgoing email including the attachment is sent to the destination mail server 7 via an encrypted communication path encrypted by TLS communication. On the other hand, if it is confirmed that the destination mail server 7 does not support TLS communication, the attachment is separated from the outgoing email and sent to the attachment storage server 4 according to the attachment sending method preset in the outgoing email sending setting storage unit 304. Alternatively, the attachment is encrypted and compressed into a password-protected compressed file, reattached to the outgoing email, and sent to the destination mail server 7. The outgoing email from which the attachment has been removed is sent to the destination mail server 7 via an unencrypted communication path that is not encrypted by TLS communication.

[0057] The encrypted communication determination process control unit 301 is configured from the above-mentioned control unit 30, and controls a series of operations of the TLS communication determination process unit 300. In other words, this encrypted communication determination process control unit 301 controls the operations of each element included in the TLS communication determination process unit 300. This encrypted communication determination process control unit 301 switches the attachment sending method based on the TLS communication support information of the destination mail server 7 acquired by the TLS communication support information inquiry unit 308. This sending method includes a method of sending the attachment to the attachment storage server 4, and a method of encrypting and compressing the attachment into a password-protected compressed file and then sending it to the destination mail server 7.

[0058] The outgoing mail sending setting screen providing unit 302 provides a screen for setting the sending method of attachments when the destination mail server 7 does not support TLS communication and the sending method of outgoing mail with attachments removed.

[0059] 3 is a schematic diagram of an outgoing mail sending setting screen 345 for setting the sending method of attachments when the destination mail server 7 does not support TLS communication and the sending method of outgoing mail with attachments removed. At the top of this outgoing mail sending setting screen 345 is a setting section 346 for the sending method of attachments, and below that is a setting section 347 for the sending method of outgoing mail with attachments removed.

[0060] In the attachment sending method setting section 346, it is possible to select and set the method for sending attachments when the destination mail server 7 does not support TLS communication. As shown in this figure, it is possible to select and set either to upload the attachment to the attachment storage server 4 and send it, or to compress the attachment into a password-protected compressed file and send the outgoing email with this password-protected compressed file reattached to the destination mail server 7.

[0061] In the setting section 347 for the sending method of outgoing mail from which attachments have been removed, it is possible to select and set the sending method of outgoing mail from which attachments have been removed when the destination mail server 7 does not support TLS communication. As shown in this figure, from top to bottom, there are options arranged: "Hold for a specified time and send outgoing mail after the specified time has elapsed," "Send outgoing mail after adding a specified email address to the Bcc (Blind Carbon Copy) of the outgoing mail," "Cancel sending of outgoing mail," "Send outgoing mail after approval by a specified approver," "Send outgoing mail and notify a pre-registered email address," and "Send outgoing mail immediately," and one of these options can be selected and set.

[0062] In addition, there are provided a column for setting the hold time when selecting "Hold for a specified time and send the outgoing email after the specified time has elapsed," a column for setting the email address to be added to the Bcc when selecting "Send the outgoing email after adding the email address to the Bcc of the outgoing email," a column for setting the email address of the approver when selecting "Send the outgoing email after the approver's approval," and a column for setting the email address to be notified when selecting "Send the outgoing email and notify the email address to be notified."

[0063] This outgoing mail sending setting screen 345 is provided to the sender terminal 5, the administrator terminal 6, etc., and through this setting screen 345, the sending method of the attached file and the sending method of the outgoing mail from which the attached file has been removed are set.

[0064] 2 accepts settings for the method of sending attachments when the destination mail server 7 does not support TLS communication, and settings for the method of sending outgoing mail from which attachments have been removed, which are set on the outgoing mail sending settings screen 345. The settings accepted by this outgoing mail sending settings acceptance unit 303 are set and registered in the outgoing mail sending settings holding unit 304.

[0065] Settings for the method of sending attachments when the destination mail server 7 does not support TLS communication and settings for the method of sending outgoing mail from which attachments have been removed are stored in the outgoing mail sending setting storage unit 304. These settings may be made from the sender terminal 5 or the administrator terminal 6 as described above, or may be set in advance when the email sending system 2 is installed.

[0066] When the destination mail server 7 does not support TLS communication, the attachment can be sent to the attachment storage server 4 as described above and provided from the attachment storage server 4, or the attachment can be compressed into a password-protected file and sent to the destination mail server 7.

[0067] In addition, when the destination mail server 7 does not support TLS communication, various settings are possible as a method for sending the outgoing mail from which attachments have been removed, such as holding for a specified time and sending the outgoing mail after the specified time has elapsed, sending the outgoing mail after adding a specified email address to the Bcc of the outgoing mail, canceling the sending of the outgoing mail, sending the outgoing mail after approval by a specified approver, sending the outgoing mail and notifying a pre-registered email address, or sending the outgoing mail immediately.

[0068] The attached file detection unit 306 detects whether or not an attached file is attached to the outgoing mail accepted by the outgoing mail acceptance unit 32 .

[0069] The TLS communication support information inquiry unit 308 inquires of the destination mail server 7 of the outgoing mail and acquires TLS communication support information including information on whether the destination mail server 7 supports TLS. For example, it sends an EHLO command to the destination mail server 7 and detects a response from the destination mail server 7 to that command.

[0070] The TLS communication support status determination unit 310 determines whether the destination mail server 7 supports TLS based on the TLS communication support information acquired by the TLS communication support information inquiry unit 308. The conditions for determining that the destination mail server 7 does not support TLS may include not only incompatibility with TLS, but also high security risks, such as a low encryption version, a certificate that cannot be traced back to the root (root certificate), an expired certificate, or the use of a vulnerable cipher, even if the server supports TLS.

[0071] The attachment separation unit 312 separates the attachment from an outgoing mail with an attachment, and divides the outgoing mail into the attachment and the outgoing mail from which the attachment has been removed.

[0072] The compression / decompression password generating unit 314 generates a compression / decompression password for compressing the separated attachment file into a password-protected compressed file. This compression / decompression password also serves as the password for decompressing the password-protected compressed file.

[0073] The compression / decompression password can be generated by, for example, generating it from a randomly generated character string, generating it from a character string specified from the sender terminal 5, or using a one-time password.

[0074] When multiple attachments are attached to an outgoing email, these attachments may be combined into a single password-protected compressed file, or the multiple attachments may be compressed using a single compression / decompression password generated by the compression / decompression password generation unit 314.

[0075] A compression / decompression password notification email separate from the outgoing email containing the compression / decompression password is created by the sending mail server 3 and sent to the destination mail server 7.

[0076] The attachment compression unit 316 applies the compression / decompression password generated by the compression / decompression password generation unit 314 to encrypt / compress the attachment into a password-protected compressed file. As described above, when multiple attachments are attached to an outgoing email, these multiple attachments may be combined into a single compressed file.

[0077] If the destination mail server 7 supports TLS communication, an encrypted communication path encrypted by highly secure TLS communication can be selected to send the attachment to the destination mail server 7. Furthermore, a high level of security is also ensured for the transmission path in which the attachment is sent to the attachment storage server 4, where it is stored, and then provided from the attachment storage server 4. Therefore, if an outgoing email containing an attachment can be sent over an encrypted communication path encrypted by TLS communication, or if the attachment is sent to the attachment storage server 4, the attachment can be sent safely without being encrypted and compressed into a password-protected compressed file. Therefore, in such cases, it is not necessary to encrypt the attachment into a password-protected compressed file, and the attachment may be sent as is without being encrypted and compressed.

[0078] The outgoing mail body appending unit 318 appends text to the body of the outgoing mail under the control of the encrypted communication determination processing control unit 301. Based on the TLS communication support information of the destination mail server 7 acquired by the TLS communication support information inquiry unit 308, text indicating whether the destination mail server 7 supports TLS is appended to the body of the outgoing mail. For example, if the destination mail server 7 supports TLS, text such as "Sent via an encrypted mail communication path (TLS communication)" or "This mail was sent via an encrypted communication path encrypted by TLS communication" is appended to the body. On the other hand, if the destination mail server 7 does not support TLS, text such as "Sent via an unencrypted mail communication path (TLS communication)" or "This mail was sent via an unencrypted communication path not encrypted by TLS communication" is appended to the body.

[0079] In addition, the download URL indicating the location (address) of the attachment on the attachment storage server 4, which is generated by the download URL generation unit 326 described below, and the download password for downloading the attachment from the attachment storage server 4, which is generated by the download password generation unit 328, are also added to the body of the outgoing email by the outgoing email body appending unit 318.

[0080] FIG. 4 is a schematic diagram showing an example of a display screen of an outgoing email including text added by the outgoing email body adding unit 318. Such an email display screen is displayed on the destination terminal 8. FIG. 4(a) shows a screen of an email sent via an unencrypted communication path that is not encrypted by TLS communication, and FIG. 4(b) shows a screen of an email sent via an encrypted communication path that is encrypted by TLS communication. The added text 350 added by the outgoing email body adding unit 318 is made up of an encrypted / unencrypted transmission indicator 352 that indicates whether the email was sent via an encrypted communication path that is encrypted by TLS communication or an unencrypted communication path that is not encrypted by TLS communication, an attachment download guide indicator 354 that provides guidance on downloading the attachment from the attachment storage server 4, a download URL indicator 356 that displays the download URL, and the like. In addition, an outgoing email body 360 is displayed below the added text 350.

[0081] The compressed file reattachment unit 320 shown in FIG. 2 reattaches the password-protected compressed file to the outgoing mail from which the attachment was removed.

[0082] The password-containing email creation unit 321 creates a password-containing email (compression / decompression password notification email) that notifies the destination terminal 8 of the compression / decompression password generated by the compression / decompression password generation unit 314. The password-containing email contains the compression / decompression password. This password-containing email is then sent to the destination mail server 7 as a separate mail from the outgoing email from the sender terminal 5.

[0083] The sender terminal notification unit 322 notifies the sender terminal 5 that has sent the outgoing email, based on the control of the encrypted communication determination processing control unit 301. The sender terminal 5 is notified of content indicating whether the outgoing email was sent to the destination mail server 7 via an encrypted communication path encrypted by TLS communication. For example, if the outgoing email was sent to the destination mail server 7 via an encrypted communication path encrypted by TLS communication, the sender terminal 5 is notified of content such as "Sent via an encrypted email communication path (TLS communication)" or "This email was sent via an encrypted communication path encrypted by TLS communication." On the other hand, if the outgoing email was sent via an unencrypted communication path that is not encrypted by TLS communication, the sender terminal 5 is notified of content such as "Sent via an unencrypted email communication path (TLS communication)" or "This email was sent via an unencrypted communication path that is not encrypted by TLS communication."

[0084] The administrator terminal notification unit 324 notifies the administrator terminal 6 of the transmission result of the outgoing email sent from the sender terminal 5 under the control of the encrypted communication determination processing control unit 301. The administrator terminal 6 is notified of the content indicating whether the outgoing email was sent to the destination mail server 7 via an encrypted communication path encrypted by TLS communication.

[0085] When an attached file is sent to the attached file storage server 4 for storage, the download URL generation unit 326 generates a download URL indicating the location (address) of the attached file in the attached file storage server 4.

[0086] The generated download URL is added to the body of the outgoing mail by the outgoing mail body adding unit 318.

[0087] The download password generating unit 328 generates a download password for downloading an attachment stored in the attachment storage server 4.

[0088] The generated download password is added to the body of the outgoing mail by the outgoing mail body adding unit 318.

[0089] The attachment file upload unit 330 sends the attachment file to the attachment file storage server 4. At this time, the download URL generated by the download URL generation unit 326 and the download password generated by the download password generation unit 328 are also sent to the attachment file storage server 4.

[0090] The sent mail history storage unit 332 stores sending history information of sent mail sent from the sender terminal 5. The sending history information includes TLS communication support information of the destination mail server 7 and the determination result of whether or not it supports TLS. The sending history information also includes information on whether or not the mail was sent to the destination mail server 7 via an encrypted communication path encrypted by TLS communication, sender information, and destination information. Sending history information is stored for each sent mail sent from the sender terminal 5.

[0091] The sent mail history providing unit 334 provides the sending history information stored in the sent mail history storage unit 332. In response to a request for sending history information sent from the sender terminal 5 or the administrator terminal 6, the requested sending history information is provided to the request source.

[0092] The sent email history report creation unit 336 creates a sent email history report based on the sending history information for each of the multiple sent emails stored in the sent email history storage unit 332. This sent email history report includes the number of encrypted emails, which is the number of sent emails sent to the destination mail server 7 via an encrypted communication path encrypted by TLS communication; the number of unencrypted emails, which is the number of sent emails sent via an unencrypted communication path not encrypted by TLS communication; and personal data, which aggregates the percentage of the number of encrypted emails and the number of unencrypted emails out of the total number of sent emails, for each sender and recipient, as well as statistical information data, which aggregates the personal data of multiple senders and multiple recipients. The sent email history report also includes a graph display, which displays the number and percentage of each destination and sender for communications via an encrypted communication path encrypted by TLS communication or communications via an unencrypted communication path not encrypted by TLS communication. For example, the graph display may include a heat map or statistical information (statistical chart). Here, statistical charts refer to graphs and tables used to organize, visualize, and analyze multiple pieces of statistical data.

[0093] The sent mail history report providing unit 338 provides the sent mail history report created by the sent mail history report creating unit 336. In response to a request for a sent mail history report from the manager terminal 6, the sent mail history report is provided to the manager terminal 6 that made the request. Then, when the manager terminal 6 receives the sent mail history report, the sent mail history report including, for example, heat map generation and statistical information (statistical charts) display is displayed on the screen of the manager terminal 6.

[0094] Pseudo screen creation unit 340 creates a pseudo display screen on which text has been added to the text of the outgoing email by outgoing email text appending unit 318. This pseudo screen creation unit 340 creates a pseudo screen that contains a pseudo representation of the text of the email text after appending by outgoing email text appending unit 318, assuming that the outgoing email from sender terminal 5 has been sent over an encrypted communication path encrypted by TLS communication, or assuming that the email has been sent over an unencrypted communication path not encrypted by TLS communication. This pseudo screen creation unit 340 can create a pseudo screen regardless of whether the outgoing email has been sent or not.

[0095] In addition, this pseudo screen creation unit 340 creates a pseudo screen by simulating the text of the email body to which the download URL and download password have been added by the outgoing email body addition unit 318, assuming that the attached file has been sent to the attachment file storage server 4.

[0096] The pseudo screen providing unit 342 provides a pseudo screen of the outgoing email created by the pseudo screen creating unit 340. In response to a pseudo screen provision request from the administrator terminal 6, the pseudo screen is provided to the administrator terminal 6 that is the request source. Then, when the administrator terminal 6 receives the pseudo screen, the pseudo screen is displayed on the screen of the administrator terminal 6. In this way, the pseudo screen can be checked in advance without sending the outgoing email.

[0097] The above is an explanation of the functional block diagram of the sending mail server 3.

[0098] In this sender's mail server 3, when the attachment detection unit 306 detects that an attachment is attached to an outgoing mail, the encrypted communication determination processing control unit 301 causes the TLS communication support information inquiry unit 308 to acquire TLS communication support information for the destination mail server 7. If it is determined from the acquired TLS communication support information that the destination mail server 7 supports TLS, the encrypted communication control unit 301 causes the outgoing mail sending unit 36 ​​to select an encrypted communication path encrypted by TLS and send the outgoing mail including the attachment to the destination mail server 7. On the other hand, if it is determined that the destination mail server 7 does not support TLS, the encrypted communication determination processing control unit 301 causes the attachment upload unit 330 to send the attachment-separated outgoing mail to the attachment storage server 4, and causes the outgoing mail sending unit 36 ​​to send the outgoing mail from which the attachment has been removed to the destination mail server 7 via an unencrypted communication path not encrypted by TLS. Alternatively, the encrypted communication determination processing control unit 301 compresses the attachment separated from the outgoing mail into a password-protected compressed file, and causes the outgoing mail sending unit 36 ​​to send the outgoing mail to which the password-protected compressed file has been reattached to the destination mail server 7 via an unencrypted communication path not encrypted by TLS.

[0099] 5 is a schematic functional block diagram of the attachment file storage server 4 included in the email transmission system 2. This attachment file storage server 4 stores attachment files and provides the stored attachment files in response to a request for providing the attachment files.

[0100] The attachment storage server 4 is configured to include an attachment storage server control unit 40, an attachment reception unit 41, an attachment storage unit 42, a download URL reception unit 43, a download password reception unit 44, an attachment provision request reception unit 45, a download password confirmation unit 46, an attachment provision unit 47, and a communication unit 48.

[0101] The attachment storage server control unit 40 is configured to include a CPU, an auxiliary storage device which is a nonvolatile storage device, and a RAM (not shown). The CPU executes programs and performs arithmetic processing, and the attachment storage server control unit 40 controls each element that constitutes the attachment storage server 4.

[0102] The attachment file receiving unit 41 receives attachment files sent from the sending mail server 3 under the control of the attachment file storage server control unit 40 .

[0103] The attached file storage unit 42 stores the attached file received by the attached file receiving unit 41.

[0104] The download URL receiving unit 43 receives and stores the download URL sent from the sending mail server 3.

[0105] The attached files stored in the attached file storage unit 42 are associated with the download URLs accepted by the download URL acceptance unit 43, and the association information between the attached files and the download URLs is stored in the attached file storage unit 42. When this download URL is accessed from an external destination terminal 8 or the like that is the source of the attachment request, the attached file associated with this download URL is downloaded.

[0106] The download password acceptance unit 44 accepts and stores the download password sent from the sending mail server 3. This download password is a password that is required to be entered when downloading an attachment, and if it matches the entered password, the download is permitted.

[0107] The attachment request receiving unit 45 receives a request to provide an attachment file from an external device such as the destination terminal 8. This request is generated by accessing a download URL from an external device that is the source of the request.

[0108] A download password confirmation part 46 receives an input download password sent from a source requesting the provision of the attachment file, compares the received input password with the download password received by a download password reception part 44, and permits downloading of the attachment file if they match, and prohibits downloading if they do not match.

[0109] The attachment providing unit 47 provides the attachment by downloading it to the request source that sent the provision request.

[0110] The communication unit 48 transmits and receives data to and from the outside.

[0111] When the sending mail server 3 confirms that the destination mail server 7 does not support TLS, the encrypted communication determination processing control unit 301 of the sending mail server 3 sends the attachment separated from the outgoing email from the attachment upload unit 330 to the attachment storage server 4.

[0112] In the attachment storage server 4, attachments sent from the sending mail server 3 are accepted by attachment acceptance unit 41, and the accepted attachments are stored in attachment storage unit 42. After the attachments have been stored in attachment storage unit 42 in this way, for example, if a destination terminal 8 or the like accesses a download URL and sends a request to provide the attachment, this provision request is accepted by attachment provision request acceptance unit 45. Next, when an input download password is sent from the destination terminal 8 or the like that is the source of the provision request, it is accepted by download password confirmation unit 46 and determined whether it matches the correct download password. If they match, downloading of the attachment is permitted, and the attachment is provided from attachment provision unit 47 to the destination terminal 8 or the like that is the source of the provision request.

[0113] Next, the operation of the email system 1 including the email transmission system 2 according to the first embodiment of the present invention will be described.

[0114] Figure 6 is a schematic diagram showing the flow of sending an e-mail in this e-mail system 1. However, if the destination mail server 7 does not support TLS, it shows the flow of sending an attachment to the attachment storage server 4. It also shows the setting flow for immediately sending an outgoing e-mail with attachments removed if the destination mail server 7 does not support TLS.

[0115] First, a mail to be sent is created using the sender terminal 5 (step S100), and the created mail to be sent is sent to the sending mail server 3 (step S101).

[0116] The sending mail server 3 receives an outgoing mail sent from the sender terminal 5 (step S200), and checks whether or not an attachment file is attached to the received outgoing mail (step S201).

[0117] If no attachment file is attached (No in step S201), the accepted outgoing mail is sent to the destination mail server 7 (step S230).

[0118] On the other hand, if an attachment is included (Yes in step S201), the sending mail server 3 inquires of the destination mail server 7 as to whether or not it supports TLS (step S202). When the destination mail server 7 receives this inquiry (step S400), it sends TLS communication support information to the sending mail server 3 (step S401).

[0119] When the sending mail server 3 acquires the TLS communication support information (step S203), it determines whether the destination mail server 7 supports TLS based on the acquired TLS communication support information (step S204).

[0120] If the destination mail server 7 supports TLS (Yes in step S204), a statement is added to the body of the outgoing mail indicating that the outgoing mail will be sent over an encrypted communication path encrypted by TLS (step S220). Then, the outgoing mail including the attachment is sent to the destination mail server 7 over the encrypted communication path encrypted by TLS (step S221). Then, the sender terminal 5 is notified that the outgoing mail including the attachment has been sent over an encrypted communication path encrypted by TLS (step S222).

[0121] On the other hand, if the destination mail server 7 does not support TLS (No in step S204), a note is added to the body of the outgoing mail indicating that the outgoing mail will be sent over an unencrypted communication path that is not encrypted by TLS communication (step S205). After that, the attachment is separated from the outgoing mail (step S206), and the separated attachment is sent to the attachment storage server 4 (step S207). The attachment storage server 4 accepts the sent attachment (step S300) and stores it (step S301).

[0122] Next, the sender's mail server 3 sends the outgoing mail from which the attachment has been removed to the destination's mail server 7 via a non-encrypted communication path that has not been encrypted by TLS (step S208). After that, the sender's terminal 5 is notified that the outgoing mail from which the attachment has been removed has been sent without encryption (step S209).

[0123] When the destination mail server 7 receives the outgoing mail from the sender mail server 3 with the attachment removed, it stores the outgoing mail (step S402). When the destination terminal 8, which is the destination of the outgoing mail, requests the destination mail server 7 to view the outgoing mail, the destination mail server 7 sends the stored outgoing mail addressed to the destination terminal 8 to the destination terminal 8 (step S403).

[0124] The destination terminal 8 receives the outgoing mail sent from the destination mail server 7 (step S500) and displays it on the screen. When the destination terminal 8 makes a request to provide the attached file stored in the attachment file storage server 4 (step S501), the attachment file storage server 4 that receives this request (step S302) provides the attached file in response to the request (step S303). The destination terminal 8 that has made the request to provide the attached file receives the attached file (step S502) and views it.

[0125] When an outgoing email is sent (step S230) without an attachment (No in step S201), the sending mail server 3 inquires of the destination mail server 7 whether it supports TLS. If the destination mail server 7 supports TLS, a note is added to the body of the outgoing email indicating that the outgoing email will be sent over an encrypted communication path encrypted by TLS. The outgoing email is then sent to the destination mail server 7 over the encrypted communication path encrypted by TLS. The sender terminal 5 is then notified that the outgoing email has been sent over an encrypted communication path encrypted by TLS. On the other hand, if the destination mail server 7 does not support TLS, a note is added to the body of the outgoing email indicating that the outgoing email will be sent over an unencrypted communication path that is not encrypted by TLS. The outgoing email is then sent to the destination mail server 7 over an unencrypted communication path that is not encrypted by TLS. The sender terminal 5 is then notified that the outgoing email has been sent unencrypted.

[0126] Figure 7 is a schematic diagram showing the flow of sending an e-mail in this e-mail system 1. However, if the destination mail server 7 does not support TLS, the diagram shows the flow of compressing the attached file into a password-protected compressed file, reattaching the compressed file to the outgoing e-mail, and sending it to the destination mail server 7. It also shows the flow of settings for immediately sending an outgoing e-mail with a password-protected compressed file attached if the destination mail server 7 does not support TLS.

[0127] First, a mail to be sent is created using the sender terminal 5 (step S150), and the created mail to be sent is sent to the sending mail server 3 (step S151).

[0128] The sending mail server 3 receives an outgoing mail sent from the sender terminal 5 (step S250), and checks whether or not an attachment file is attached to the received outgoing mail (step S251).

[0129] If no attachment file is attached (No in step S251), the accepted outgoing mail is sent to the destination mail server 7 (step S280).

[0130] On the other hand, if an attachment is included (Yes in step S251), the sending mail server 3 inquires of the destination mail server 7 as to whether or not it supports TLS (step S252). When the destination mail server 7 receives this inquiry (step S450), it sends TLS communication support information to the sending mail server 3 (step S451).

[0131] When the sending mail server 3 acquires the TLS communication support information (step S253), it determines whether or not the destination mail server 7 supports TLS based on the acquired TLS communication support information (step S254).

[0132] If the destination mail server 7 supports TLS (Yes in step S254), a statement is added to the body of the outgoing mail indicating that the outgoing mail will be sent over an encrypted communication path encrypted by TLS (step S270). Then, the outgoing mail including the attachment is sent to the destination mail server 7 over the encrypted communication path encrypted by TLS (step S271). Then, the sender terminal 5 is notified that the outgoing mail including the attachment has been sent over an encrypted communication path encrypted by TLS (step S272).

[0133] On the other hand, if the destination mail server 7 does not support TLS (No in step S254), a note is added to the body of the outgoing mail indicating that the outgoing mail will be sent via a non-encrypted communication path that is not encrypted by TLS communication (step S255). Then, the attached file is separated from the outgoing mail (step S256), and a compression / decompression password is generated by the compression / decompression password generation unit 314 (step S257). Next, the generated compression / decompression password is applied to encrypt and compress the attached file to generate a password-protected compressed file (step S258). This password-protected compressed file is reattached to the outgoing mail (step S259), and the outgoing mail with this compressed file attached is sent to the destination mail server 7 via a non-encrypted communication path that is not encrypted by TLS (step S260). Next, the email containing the compression / decompression password is sent from the sending mail server 3 to the destination mail server 7 (step S261). Thereafter, the sender terminal 5 is notified that the outgoing email with the password-protected compressed file attached has been sent via a non-encrypted communication path that has not been encrypted by TLS communication (step S262).

[0134] When the destination mail server 7 receives the outgoing mail with the password-protected compressed file attached and the mail containing the decompression password from the sender mail server 3, it stores the outgoing mail (step S452). When the destination terminal 8 that is the destination of the outgoing mail requests the destination mail server 7 to view the outgoing mail, the destination mail server 7 sends the stored outgoing mail addressed to the destination terminal 8 to the destination terminal 8 (step S453).

[0135] The destination terminal 8 receives the outgoing mail with the password-protected compressed file attached and the mail containing the decompression password sent from the destination mail server 7 (step S550). Then, the destination terminal 8 applies the decompression password to decompress the password-protected compressed file and decrypts it back into the original attached file (step S551). This decompression process allows the destination terminal 8 to view the decompressed attached file.

[0136] When an outgoing email is sent (step S280) without an attachment (No in step S251), the sending mail server 3 inquires of the destination mail server 7 whether it supports TLS. If the destination mail server 7 supports TLS, a note is added to the body of the outgoing email indicating that the outgoing email will be sent over an encrypted communication path encrypted by TLS. The outgoing email is then sent to the destination mail server 7 over the encrypted communication path encrypted by TLS. The sender terminal 5 is then notified that the outgoing email has been sent over an encrypted communication path encrypted by TLS. On the other hand, if the destination mail server 7 does not support TLS, a note is added to the body of the outgoing email indicating that the outgoing email will be sent over an unencrypted communication path that is not encrypted by TLS. The outgoing email is then sent to the destination mail server 7 over an unencrypted communication path that is not encrypted by TLS. The sender terminal 5 is then notified that the outgoing email has been sent unencrypted.

[0137] Next, the effects of the first embodiment of the present invention will be described.

[0138] According to the first embodiment, if it is confirmed that the destination mail server 7 supports TLS, an encrypted communication path encrypted by TLS is selected and the outgoing mail including the attachment is sent to the destination mail server 7, whereas if it is confirmed that the destination mail server 7 does not support TLS, the attachment is sent based on the settings of the outgoing mail sending setting storage unit 304, and the outgoing mail without the attachment is sent to the destination mail server 7 via an unencrypted communication path that is not encrypted by TLS. This makes it possible to realize an email sending system that can send attachments safely and does not cause email delivery interruptions.

[0139] Furthermore, according to the first embodiment, when the destination mail server 7 does not support TLS, the attachment can be sent either by sending the attachment to the attachment storage server 4 and providing the attachment via the attachment storage server 4, or by compressing the attachment into a password-protected compressed file, attaching the password-protected compressed file to an outgoing email, and sending it to the destination mail server 7. This allows the attachment to be sent safely. A higher level of security is ensured with the sending method using the attachment storage server 4. On the other hand, the method of attaching a password-protected compressed file to an outgoing email and sending it to the destination mail server 7 does not require the installation of the attachment storage server 4, thereby simplifying the system configuration.

[0140] Furthermore, according to the first embodiment, when the destination mail server 7 does not support TLS, the method of sending the attachment can be selected from either sending the attachment to the attachment storage server 4 and providing the attachment via the attachment storage server 4, or compressing the attachment into a password-protected compressed file, attaching the password-protected compressed file to the outgoing mail, and sending it to the destination mail server 7. This makes it easy to set the method of sending the attachment, and realizes a system that is easy to introduce and easy to use.

[0141] Furthermore, according to the first embodiment, there are multiple methods for sending outgoing mail from which attachments have been removed when the destination mail server 7 does not support TLS, and various settings are possible. Furthermore, settings can be flexibly realized according to the needs of the user.

[0142] Furthermore, according to the first embodiment, the sending method for outgoing emails from which attachments have been removed when TLS is not supported can be selected from multiple options. This allows the sending method to be easily set, realizing a system that is easy to introduce and easy to use.

[0143] Furthermore, according to this embodiment 1, a sentence indicating whether the destination mail server 7 supports TLS is added to the body of the outgoing email, so when you receive the outgoing email, you can check whether the email was sent via an encrypted communication path encrypted by TLS.

[0144] Furthermore, according to the first embodiment, it is possible to check at the sender terminal 5 of the outgoing email whether the outgoing email has been sent through an encrypted communication path encrypted by TLS.

[0145] Furthermore, according to the first embodiment, the administrator terminal 6 can check whether or not an outgoing email has been sent via an encrypted communication path encrypted by TLS.

[0146] Furthermore, according to this embodiment 1, by checking the created sent email history report, it is possible to perform a detailed analysis of the history, such as how many sent emails were sent through an encrypted communication path encrypted by TLS.

[0147] Furthermore, according to the first embodiment, it is possible to check in advance the display screen of the outgoing mail that will be delivered to the destination.

[0148] [Embodiment 2 of the Invention] In the above-described first embodiment of the present invention, when it is detected that an attachment is attached to an outgoing email, it is determined whether the destination mail server 7 supports TLS communication.

[0149] In the second embodiment of the present invention, whether or not the destination mail server 7 supports TLS communication is determined when sending an outgoing email, regardless of whether or not there is an attachment. An email transmission system 2A according to the second embodiment of the present invention will be described below, but elements that are the same as or similar to those in the email system 1 and email transmission system 2 according to the first embodiment above will be given the same reference numerals, and duplicate explanations will be omitted.

[0150] A second embodiment of the present invention will be described with reference to FIGS.

[0151] FIG. 8 is a block diagram showing a schematic configuration of an email system 1A including an email transmission system 2A according to a second embodiment of the present invention.

[0152] The configuration is the same as that of the email system 1 according to the first embodiment of the present invention (see FIG. 1), except that the attachment file storage server 4 is removed.

[0153] This e-mail transmission system 2A includes a sending mail server 3A that sends out an outgoing mail created on a sender terminal 5 to a destination mail server 7.

[0154] 9 is a schematic functional block diagram of the sending mail server 3 A. Elements related to the attachment storage server 4, such as the download URL generation unit 326, the download password generation unit 328, and the attachment upload unit 330, have been removed from the configuration of the sending mail server 3 according to the first embodiment of the present invention (see FIG. 2).

[0155] Before the sending mail server 3 sends an outgoing mail to the destination mail server 7, the sending mail server 3 determines whether the destination mail server 7 supports TLS. If the destination mail server 7 supports TLS, the sending mail server 3 selects an encrypted communication path encrypted by TLS communication and sends the outgoing mail. On the other hand, if the destination mail server 7 does not support TLS, the sending mail server 3 sends the outgoing mail based on the outgoing mail sending method preset in the outgoing mail sending setting storage unit 304.

[0156] The outgoing mail sending setting screen providing unit 302 provides a screen for setting the sending method for outgoing mail when the destination mail server 7 does not support TLS communication. Specifically, the same setting selection items as those in the setting unit 347 for the sending method for outgoing mail excluding attachments on the outgoing mail sending setting screen 345 shown in Fig. 3 are displayed on the screen as the sending method for outgoing mail. By inputting information on this screen, the sending method for outgoing mail when the destination mail server 7 does not support TLS communication can be selected and set.

[0157] The options for sending outgoing emails include "Hold for a specified time and send outgoing email after the specified time has elapsed," "Send outgoing email after adding a specified email address to the Bcc of the outgoing email," "Cancel sending outgoing email," "Send outgoing email after approval by a specified approver," "Send outgoing email and notify a pre-registered email address," and "Send outgoing email immediately." You can select one of these options to set.

[0158] This outgoing mail sending setting screen is provided to the sender terminal 5, the administrator terminal 6, etc., and the sending method of outgoing mail is set through this setting screen.

[0159] The outgoing mail sending setting acceptance unit 303 accepts the setting of the sending method of outgoing mail when the destination mail server 7 does not support TLS communication, which is set on the outgoing mail sending setting screen. The setting accepted by this outgoing mail sending setting acceptance unit 303 is set and registered in the outgoing mail sending setting holding unit 304.

[0160] Furthermore, if an outgoing email has an attachment, and the destination mail server 7 supports TLS, the outgoing email including the attachment is sent to the destination mail server 7 via an encrypted communication path encrypted based on TLS. On the other hand, if the destination mail server 7 does not support TLS, the attachment is encrypted and compressed into a password-protected compressed file, and this password-protected compressed file is reattached to the outgoing email and sent to the destination mail server 7 via an unencrypted communication path that is not encrypted by TLS. Next, an email containing the compression / decompression password to the same destination is sent to the destination mail server 7.

[0161] If the destination mail server 7 supports TLS, the attachment is sent safely over an encrypted communication path encrypted by TLS, and if the destination mail server 7 does not support TLS, the attachment is encrypted and compressed into a password-protected compressed file before being sent, so the attachment can be sent safely.

[0162] The sending mail server 3A has an outgoing mail reception unit 32 that receives the created outgoing mail from the sender terminal 5, a TLS communication compatibility information inquiry unit 308 that acquires TLS communication compatibility information from the destination mail server 7, including information on whether the destination mail server 7 of the outgoing mail supports TLS, an outgoing mail sending setting storage unit 304 that pre-stores settings for the sending method of the outgoing mail when the destination mail server 7 does not support TLS, an outgoing mail sending unit 36 ​​that sends the outgoing mail to the destination mail server 7, and an encrypted communication determination processing control unit 301 that controls the sending operation of the outgoing mail based on the TLS communication compatibility information acquired by the TLS communication compatibility information inquiry unit 308.

[0163] This encrypted communication determination processing control unit 301 causes the TLS communication support information inquiry unit 308 to acquire TLS communication support information of the destination mail server 7, and if it is confirmed from the acquired TLS communication support information that the destination mail server 7 supports TLS, it selects an encrypted communication path encrypted by TLS and causes the outgoing mail sending unit 36 ​​to send the outgoing mail to the destination mail server 7. On the other hand, if it is confirmed that the destination mail server 7 does not support TLS, it causes the outgoing mail sending unit 36 ​​to send the outgoing mail through an unencrypted communication path that is not encrypted by TLS, based on the settings of the outgoing mail sending setting holding unit 304.

[0164] The sending method of the outgoing mail set in the outgoing mail sending setting holding unit 304 can be selected from among the following: to hold for a specified time and then send the outgoing mail after the specified time has elapsed; to send the outgoing mail after adding a specified email address to the Bcc of the outgoing mail; to cancel sending the outgoing mail; to send the outgoing mail after approval by a specified approver; to send the outgoing mail and notify a pre-registered email address; or to send the outgoing mail immediately.

[0165] Next, the operation of the electronic mail system 1A including the electronic mail transmission system 2A according to the second embodiment of the present invention will be described.

[0166] FIG. 10 is a schematic diagram showing the flow of sending an e-mail in this e-mail system 1A.

[0167] First, a mail to be sent is created using the sender terminal 5 (step S600), and the created mail to be sent is sent to the sending mail server 3A (step S601).

[0168] When the sending mail server 3A receives an outgoing mail sent from the sender terminal 5 (step S700), it queries the destination mail server 7 as to whether it supports TLS or not (step S701). When the destination mail server 7 receives this query (step S800), it sends TLS communication support information to the sending mail server 3A (step S801).

[0169] When the sending mail server 3 acquires the TLS communication support information (step S702), it determines whether the destination mail server 7 supports TLS based on the acquired TLS communication support information (step S703).

[0170] If the destination mail server 7 supports TLS (Yes in step S703), a statement is added to the body of the outgoing mail indicating that the outgoing mail will be sent over an encrypted communication path encrypted by TLS (step S710). The outgoing mail is then sent to the destination mail server 7 over the encrypted communication path encrypted by TLS (step S711). The sender terminal 5 is then notified that the outgoing mail has been sent over an encrypted communication path encrypted by TLS (step S712).

[0171] On the other hand, if the destination mail server 7 does not support TLS (No in step S703), a note is added to the body of the outgoing mail indicating that the outgoing mail will be sent via an unencrypted communication path that is not encrypted by TLS communication (step S704). The outgoing mail is then sent to the destination mail server 7 using the outgoing mail sending method set in the outgoing mail sending setting storage unit 304 (step S705). However, depending on the setting in the outgoing mail sending setting storage unit 304, the sending of the outgoing mail may be canceled. The outgoing mail sending method set in the outgoing mail sending setting storage unit 304 is one of the following: (1) hold the outgoing mail for a predetermined time and then send it after the predetermined time has elapsed; (2) add a predetermined email address to the Bcc field of the outgoing mail and then send the outgoing mail; (3) cancel the sending of the outgoing mail; (4) send the outgoing mail after approval by a predetermined approver; (5) send the outgoing mail and notify a pre-registered email address; or (6) immediately send the outgoing mail.

[0172] Thereafter, the sender terminal 5 is notified that the outgoing mail has been sent via a non-encrypted communication path that has not been encrypted by TLS communication (step S706).

[0173] When the destination mail server 7 receives the outgoing mail from the sender mail server 3A, it stores the outgoing mail (step S802). When the destination terminal 8, which is the destination of the outgoing mail, requests the destination mail server 7 to view the outgoing mail, the destination mail server 7 sends the stored outgoing mail addressed to the destination terminal 8 to the destination terminal 8 (step S803).

[0174] The destination terminal 8 receives the sent outgoing mail (step S900).

[0175] Next, the effects of the second embodiment of the present invention will be described.

[0176] According to the second embodiment, if it is confirmed that the destination mail server 7 supports TLS, an encrypted communication path encrypted by TLS is selected and the outgoing mail is sent to the destination mail server 7. On the other hand, if it is confirmed that the destination mail server 7 does not support TLS, the outgoing mail is sent to the destination mail server 7 through an unencrypted communication path not encrypted by TLS based on the settings in the outgoing mail sending setting storage unit 304. As a result, if the destination mail server 7 supports TLS, the outgoing mail is sent securely using TLS communication, and if the destination mail server 7 does not support TLS, the outgoing mail is sent using a preset sending method. This allows the sender or administrator of the outgoing mail to know in advance the security when the destination mail server 7 does not support TLS communication. Furthermore, an email sending system can be realized that does not cause email interruptions.

[0177] Furthermore, according to the second embodiment, there are multiple methods for sending outgoing emails when the destination mail server 7 does not support TLS, and various settings are possible. Also, settings can be flexibly realized according to the needs of users such as senders and administrators of outgoing emails.

[0178] Furthermore, according to the second embodiment, when the destination mail server 7 does not support TLS, the sending method for outgoing mail can be selected from multiple options. This allows the sending method to be easily set, realizing a system that is easy to introduce and easy to use. [Explanation of symbols]

[0179] 1, 1A... E-mail system, 2, 2A... E-mail transmission system, 3, 3A... Sender mail server, 4... Attachment file storage server, 5... Sender terminal, 6... Administrator terminal, 7... Destination mail server, 8... Destination terminal, 9... Communication line, 30... Control unit, 32... Sending mail reception unit, 34... Destination detection unit, 36... Sending mail sending unit, 38... Communication unit, 300, 300A... TLS communication determination processing unit (encrypted communication determination processing unit), 301... Encrypted communication determination processing control unit, 3 02...Outgoing mail sending setting screen providing unit, 303...Outgoing mail sending setting receiving unit, 304...Outgoing mail sending setting holding unit, 306...Attachment detection unit, 308...TLS communication support information inquiry unit (encrypted communication support information inquiry unit), 310...TLS communication support status determination unit (encrypted communication support status determination unit), 312...Attachment separation unit, 314...Compression / decompression password generation unit, 316...Attachment compression unit, 318...Outgoing mail body appending unit, 320...Compressed file replay unit Attachment unit, 321...password-containing email creation unit, 322...sender terminal notification unit, 324...administrator terminal notification unit, 326...download URL generation unit, 328...download password generation unit, 330...attachment upload unit, 332...sent email history storage unit, 334...sent email history providing unit, 336...sent email history report creation unit, 338...sent email history report providing unit, 340...pseudo screen creation unit, 342...pseudo screen providing unit, 350...addendum, 352...encrypted / unencrypted transmission display, 354...attachment download guide display, 356...download URL display, 360...email body, 40...attachment storage server control unit, 41...attachment reception unit, 42...attachment storage unit, 43...download URL reception unit, 44...download password reception unit, 45...attachment provision request reception unit, 46...download password confirmation unit, 47...attachment provision unit, 48...communication unit

Claims

1. An electronic mail transmission system including a sending mail server that sends outgoing mail created on a sender terminal to a destination mail server, The sending mail server: an outgoing mail receiving unit that receives the created outgoing mail from the sender terminal; an attachment detection unit that detects whether or not an attachment is attached to the received outgoing email; an encrypted communication support information inquiry unit that acquires encrypted communication support information from the destination mail server, the encrypted communication support information including information on whether the destination mail server of the outgoing mail supports encrypted communication; an attachment separation unit that separates the attachment from the outgoing email and divides the outgoing email into the attachment and the outgoing email from which the attachment has been removed; a sending mail sending setting storage unit that stores in advance a setting for a sending method for safely sending the attachment file when the destination mail server does not support the encrypted communication; an outgoing mail sending unit that sends the outgoing mail to the destination mail server; an encrypted communication determination processing control unit that controls a sending operation of the outgoing mail based on the encrypted communication compatibility information acquired by the encrypted communication compatibility information inquiry unit, The encrypted communication determination processing control unit When the attachment detection unit detects that the attachment is attached to the outgoing email, the encrypted communication support information inquiry unit acquires the encrypted communication support information of the destination mail server, When it is confirmed from the acquired encrypted communication support information that the destination mail server supports the encrypted communication, an encrypted communication path encrypted by the encrypted communication is selected and the outgoing mail including the attachment is sent to the destination mail server by the outgoing mail sending unit, When it is confirmed that the destination mail server does not support the encrypted communication, the attachment separated from the outgoing mail by the attachment separation unit is sent based on the setting of the outgoing mail sending setting holding unit, and the outgoing mail from which the attachment has been removed is sent to the outgoing mail sending unit via an unencrypted communication path that is not encrypted by the encrypted communication toward the destination mail server, The encrypted communication support information includes: An encrypted version of the encrypted communication and a cipher suite of the encrypted communication are included; An email sending system characterized in that when it is determined that there is a high security risk based on the encryption version and the cipher included in the cipher suite, even if the destination mail server supports the encrypted communication, the encrypted communication determination processing control unit determines that the destination mail server does not support the encrypted communication and sends the attachment separated from the outgoing email by the attachment separation unit based on the settings of the outgoing email sending setting storage unit.

2. an attachment file storage server that stores the attachment file and provides the stored attachment file in response to a request for providing the attachment file; The attachment file storage server an attachment file reception unit that receives the attachment file sent from the sending mail server; an attachment file storage unit that stores the received attachment file; an attachment request receiving unit that receives the request to provide the attachment stored in the attachment storage unit; an attachment providing unit that provides the attachment to a request source that has sent the provision request; The sending mail server: an attachment file upload unit that sends the attachment file to the attachment file storage server; Furthermore, the sending mail server a compression / decompression password generation unit that generates a compression / decompression password that is applied to an encryption / compression conversion that compresses the attached file into a password-protected compressed file and that is also applied to a decryption / decompression conversion that decompresses the password-protected compressed file into the attached file before compression; an attachment compression unit that applies the generated compression / decompression password to encrypt / compress the attachment into the password-protected compressed file; a compressed file re-attachment unit that re-attaches the password-protected compressed file created by the attachment file compression unit to the outgoing email from which the attachment file has been removed, The attachment file storage server the attachment receiving unit receives the attachment sent from the attachment upload unit, and stores the received attachment in the attachment storage unit, and then when the attachment provision request receiving unit receives the provision request for the attachment, the attachment providing unit provides the attachment to the request source that sent the provision request; The sending mail server: the attachment compression unit applies the compression / decompression password generated by the compression / decompression password generation unit to the attachment separated by the attachment separation unit to create the password-protected compressed file, the compressed file re-attachment unit re-attaches the created password-protected compressed file to the outgoing email from which the attachment has been removed, and then sends the outgoing email with the password-protected compressed file attached from the outgoing email sending unit to the destination email server, The sending method of the attachment file set in the sending mail sending setting storage unit is:

2. The email sending system of claim 1, wherein the system is configured to allow the user to select either of two options: send the attachment separated by the attachment separation unit from the attachment upload unit to the attachment storage server, or compress the attachment separated by the attachment separation unit into the password-protected compressed file and send the outgoing email with the password-protected compressed file attached from the outgoing email sending unit to the destination mail server.

3. The sending method of the outgoing email from which the attachment has been removed is also set in advance in the outgoing email sending setting storage unit, The encrypted communication determination processing control unit If it is confirmed that the destination mail server does not support the encrypted communication or if it is determined that the destination mail server does not support the encrypted communication, the outgoing mail from which the attachment has been removed by the attachment separation unit is sent from the outgoing mail sending unit based on the setting of the outgoing mail sending setting holding unit, The sending method of the outgoing mail from which the attachment file has been removed, which is set in the outgoing mail sending setting storage unit, is as follows: Hold the email for a predetermined time and send it after the predetermined time has elapsed. adding a predetermined email address to a blind carbon copy of the outgoing email and then sending the outgoing email; Stop sending the outgoing email; Sending the outgoing email after approval by a predetermined approver. Sending the outgoing email and notifying a pre-registered email address. Or, Immediately send the outgoing email; 3. The electronic mail transmission system according to claim 2, wherein the electronic mail transmission system is set so that either one of the above can be selected.

4. The sending mail server: a sending mail body appending unit that appends a sentence to the body of the sending mail; The encrypted communication determination processing control unit The email sending system described in claim 2, characterized in that the sending email body appending unit is controlled so that a sentence indicating whether the destination mail server supports encrypted communication or not is appended to the body of the sending email based on the encrypted communication support information of the destination mail server obtained by the encrypted communication support information inquiry unit.

5. The sending mail server: a sender terminal notification unit that notifies the sender terminal that has sent the outgoing email; The encrypted communication determination processing control unit An email sending system as described in claim 4, characterized in that the sender terminal notification unit is controlled to notify the sender terminal of information indicating whether the outgoing email has been sent to the destination mail server through the encrypted communication path.

6. an administrator terminal that manages the e-mail sending status of the sender terminal is connected to the sending mail server so as to be able to communicate with the sender terminal; The sending mail server: an administrator terminal notification unit that notifies the administrator terminal of a transmission result of the outgoing mail sent from the sender terminal; The encrypted communication determination processing control unit The electronic mail sending system according to claim 5, characterized in that the administrator terminal notification unit is controlled so as to notify the administrator terminal of whether the outgoing email has been sent to the destination mail server through the encrypted communication path.

7. The sending mail server: a sent mail history storage unit that stores, for each sent mail sent from the sender terminal, sending history information including information on whether the sent mail has been sent to the destination mail server through the encrypted communication path, sender information, and destination information; a sent mail history report creating unit that creates a sent mail history report based on the sending history information of the plurality of sent mails stored in the sent mail history storage unit; a sent mail history report providing unit that provides the sent mail history report created by the sent mail history report creating unit, The sent email history report includes: The email sending system according to claim 6, characterized in that it includes personal data compiled by sender and / or recipient, such as the number of encrypted communication emails, which is the number of outgoing emails sent to the destination mail server via the encrypted communication path, the number of unencrypted communication emails, which is the number of outgoing emails sent via the unencrypted communication path, and the ratio of the number of encrypted communication emails or the number of unencrypted communication emails to the total number of outgoing emails, or statistical information data compiled by the personal data of multiple senders and / or multiple recipients.

8. The sending mail server: a pseudo screen creating unit that creates a pseudo display screen on which the sending email body adding unit adds a sentence to the sending email body; a pseudo screen providing unit that provides a pseudo screen of the outgoing email created by the pseudo screen creating unit, An email sending system as described in claim 4, characterized in that it is possible to create a pseudo screen of the outgoing email when the destination mail server supports the encrypted communication and the outgoing email is sent through the encrypted communication path, and a pseudo screen of the outgoing email when the destination mail server does not support the encrypted communication and the outgoing email is sent through the unencrypted communication path, regardless of the sending of the outgoing email.

9. An electronic mail transmission system including a sending mail server that sends outgoing mail created on a sender terminal to a destination mail server, The sending mail server: an outgoing mail receiving unit that receives the created outgoing mail from the sender terminal; an encrypted communication support information inquiry unit that acquires encrypted communication support information from the destination mail server, the encrypted communication support information including information on whether the destination mail server of the outgoing mail supports encrypted communication; an outgoing mail sending setting storage unit that stores in advance settings for a sending method of the outgoing mail when the destination mail server does not support the encrypted communication; an outgoing mail sending unit that sends the outgoing mail to the destination mail server; an encrypted communication determination processing control unit that controls a sending operation of the outgoing mail based on the encrypted communication compatibility information acquired by the encrypted communication compatibility information inquiry unit, The encrypted communication determination processing control unit causing the encrypted communication support information inquiry unit to acquire the encrypted communication support information of the destination mail server; When it is confirmed from the acquired encrypted communication support information that the destination mail server supports the encrypted communication, an encrypted communication path encrypted by the encrypted communication is selected and the outgoing mail is sent to the destination mail server by the outgoing mail sending unit, When it is confirmed that the destination mail server does not support the encrypted communication, if the outgoing mail has an attachment, the attachment is encrypted and compressed into a password-protected compressed file and reattached to the outgoing mail, and regardless of whether the outgoing mail has an attachment or not, the outgoing mail is sent to the outgoing mail sending unit through an unencrypted communication path that is not encrypted by the encrypted communication based on the setting of the outgoing mail sending setting holding unit, The encrypted communication support information includes: An encrypted version of the encrypted communication and a cipher suite of the encrypted communication are included; An email sending system characterized in that when it is determined that there is a high security risk based on the encryption version and the cipher included in the encryption suite, even if the destination mail server supports the encrypted communication, the encrypted communication determination processing control unit sends the outgoing email based on the settings of the outgoing email sending setting storage unit, assuming that the destination mail server does not support the encrypted communication.

10. The sending method of the outgoing mail set in the outgoing mail sending setting storage unit is Hold the email for a predetermined time and send it after the predetermined time has elapsed. adding a predetermined email address to a blind carbon copy of the outgoing email and then sending the outgoing email; Stop sending the outgoing email; Sending the outgoing email after approval by a predetermined approver. Sending the outgoing email and notifying a pre-registered email address. Or, Immediately send the outgoing email; 10. The electronic mail transmission system according to claim 9, wherein the electronic mail transmission system is set so that either one of the above can be selected.

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