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).
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.
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
- 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)