A method and system for detecting postage fraud using an indexed lookup procedure is provided. The method includes generating, at a postage-issuing computer system, a unique postage indicium associated with a unique tracking number allocated to a postage transaction. The unique tracking number provides a mail piece tracking capability within the United States Postal Service (USPS). The method further includes indexing the postage transaction with the unique tracking number; and receiving, at the postage-issuing computer system, a request to validate a printed postage indicium carried on a mail piece received at the USPS. The request includes a tracking number identified from information further carried on the mail piece. The method also includes returning, to the USPS and in response to the request, a determination indicating whether the tracking number in the request matches any records stored in a transaction database.