Patent ID: 7519559

Claim:
A computer-implemented method of processing electronic messages using a stamp authority, the method comprising: receiving, from a sender, a first electronic message that is associated with a stamp and that is addressed to a user, wherein associating the stamp with the first electronic message imposes an additional transaction cost, borne by the sender, for sending the first electronic message and appends, to the first electronic message, non-display stamp information that enables determination of whether the stamp associated with the first electronic message is valid; receiving, from the sender, a second electronic message that is not associated with a stamp and that is addressed to the user, wherein sending the second electronic message that is not associated with a stamp does not impose the additional transaction cost, borne by the sender, for sending the second electronic message; identifying the non-display stamp information appended to the first electronic message; determining whether the stamp associated with the first electronic message is valid based on the identified non-display stamp information; determining whether the second electronic message is associated with a stamp; and based on a determination that the stamp associated with the first electronic message is valid and a determination that the second electronic message is not associated with a stamp: causing a user interface that is configured to display representations of electronic messages received by the user to display, in the user interface, a first representation of the first electronic message that is associated with a valid stamp, causing the user interface to display, in the user interface, a second representation of the second electronic message that is not associated with a stamp, and causing the user interface to visually distinguish, in the user interface, the displayed first representation from the displayed second representation based on the determination that the first electronic message is associated with a valid stamp and the determination that second electronic message is not associated with a stamp.