Mail_exchange_server

A mail transfer agent (MTA) (also called a mail transport agent, message transfer agent, or smtpd (short for SMTP daemon)), is a computer program or software agent that transfers electronic mail messages from one computer to another.

The term mail server is also used to mean a computer acting as an MTA that is 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.

Overview

An MTA receives mail from another MTA (relaying), from a mail user agent (MUA), thus acting as a mail submission agent (MSA), or from an MSA that got the mail from an MUA. The MTA works behind the scenes, while the user usually interacts with the MUA.

The delivery of e-mail to a user\'s mailbox typically takes place via a mail delivery agent (MDA); many MTAs have basic MDA functionality built in, but a dedicated MDA like procmail can provide more sophistication.

According to one survey, sendmail, Microsoft Exchange Server, Postfix, and Exim together control over 85% of market share for SMTP service.Security Space Mail (MX) Server Survey, 1st Aug 2007. Another survey suggests a more balanced playing field, though it included hosted email services such as Postini.MailChannels Mail Server Survey, 2006

See also

• MX record
• List of mail servers
• Comparison of mail servers
• Mail user agent
• Mail delivery agent

References

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