A method of providing for a money transfer over a network includes the steps of: providing a stamp having a face value and a lifespan both indicated on the stamp, the stamp being a string that is a concatenation of two or more fields including the face value and the lifespan, with at least one of the fields calculated according to a prescription involving a hashing or encryption of a concatenation of others of the fields or of some other field not part of the stamp; affixing the stamp to an e-mail; and allowing the recipient of the e-mail to obtain value for the stamp if the stamp is presented to a predetermined entity (such as a stamp issuer) for the stamp value within the lifespan indicated on the stamp. The stamp may comprise a concatenation of a set of fields, including a lifespan, a stamp value; and hash/encryption.