Message delivery agent

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. 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
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
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.

Invocation
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.

List of MDA software for Unix-like platforms

 * 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