Introduction

Within Internet message handling services (MHS), a message transfer agent or mail transfer agent (MTA) or mail relay is a computer process or software agent that transfers electronic mail messages from one computer to another, in single hop application-level transactions. A MTA implements both the client (sending) and server (receiving) portions of the Simple Mail Transfer Protocol.

The term mail server is also loosely used to mean a computer acting as an MTA by running the appropriate software. The term mail exchanger (MX), in the context of the Domain Name System formally refers to an IP address assigned to a device hosting a mail server, and by extension also indicates the server itself.

References

1. http://en.wikipedia.org/wiki/Message_transfer_agent