Message delivery agent

Computer software that delivers email to a mailbox

A message delivery agent (MDA), or mail delivery agent, is a computer software component that is responsible for the delivery of e-mail messages to a local recipient's mailbox.[1] It is also called a local delivery agent (LDA).

Within the Internet mail architecture, local message delivery is achieved through a process of handling messages from the message transfer agent, and storing mail into the recipient's environment (typically a mailbox).

## Implementation

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Many mail handling software products bundle multiple message delivery agents with the message transfer agent component, providing for site customization of the specifics of mail delivery to a user.

### Unix

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On Unix-like systems, procmail and maildrop are the most popular MDAs. The Local Mail Transfer Protocol (LMTP) is a protocol that is frequently implemented by network-aware MDAs.[citation needed]

#### Invocation

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The mail delivery agent is generally not started from the command line, but is usually invoked by mail delivery subsystems, such as a mail transport agent, or a mail retrieval agent.

### Unix-like

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* Cyrus IMAP \- A mail server suite that includes a mail delivery agent
* dovecot \- A mail server suite that includes a mail delivery agent
* fetchmail \- Primarily a Mail retrieval agent (MRA)
* getmail \- simpler, more secure, modern fetchmail alternative
* fdm — modern replacement for both fetchmail and procmail from the author of tmux
* maildrop or courier-maildrop - traditional procmail replacement, part of Courier Mail Server, but can also be used with other mail servers
* procmail \- old, but still used
* bin/mail, the MDA part of Sendmail \- Sendmail is one of the oldest email packages
* Sieve mail filtering language \- a standardised mail filtering language; also, a modern replacement for procmail from the GNU Mailutils package

## See also

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* Message transfer agent (MTA)
* Mail retrieval agent (MRA)
* Message submission agent (MSA)
* Message user agent (MUA) a.k.a. email client
* E-mail agent (infrastructure) (MxA)

## References

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1. ^ RFC 5598, Internet Mail Architecture, D. Crocker (July 2009)