An eMstamp is a data token having a monetary value based on a number of imbedded credits. It is used with mail servers to govern the sending and delivery of e-mail.

eMstamp also describes the system of implementing charges and credits at the MTAs (Message Transfer Agents), the mail servers maintained by ISPs (Internet Service Providers). Through a software module, eMstamp uses the standard SMTP protocol to govern message transfers by requiring a number of monetary credits from the sending MTA before messages are accepted by a receiving MTA.