A method and system for using an indexing identifier (such as, e.g., a tracking identifier or the combination of a postage vendor ID, user account, and piece count) to decrease the size of the postage indicium transmitted to an end user computer, or eliminate transmission of the postage indicium altogether, is provided. When the postage indicium for the end user computer is generated, it is stored, and the indexing identifier, rather than the postage indicium, is transmitted to the end user computer. The indexing identifier is applied to a mail piece, which is then scanned by the postal authority. The postal authority can obtain the stored postage indicium by reference to the indexing identifier. In this manner, the postal authority has access to the postage indicium without having to apply it to the mail piece. The indexing identifiers can optionally be used to index sender identification information for verifying that the sender of a mail piece is a trusted individual or entity.