A mail delivery agent or message delivery agent (MDA) is a computer software component that is responsible for the delivery of e-mail

E-mail

Electronic mail, commonly known as email or e-mail, is a method of exchanging digital messages from an author to one or more recipients. Modern email operates across the Internet or other computer networks. Some early email systems required that the author and the recipient both be online at the...

 messages to a local recipient's mailbox

Email mailbox

An email box is the equivalent of a letter box for electronic mail. It is the destination where electronic mail messages are delivered.-Definitions:...

. Also called an LDA, or local delivery agent.

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

Email mailbox

An email box is the equivalent of a letter box for electronic mail. It is the destination where electronic mail messages are delivered.-Definitions:...

).

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

Unix-like

A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....

 systems, procmail

Procmail

procmail is a mail delivery agent capable of sorting incoming mail into various directories and filtering out spam messages. Procmail is widely used on Unix-based systems and stable, but no longer maintained; users who wish a maintained program are advised to use an alternative MDA, such as...

 and maildrop

Maildrop

maildrop is a Mail delivery agent used by the Courier Mail Server. The maildrop MDA also includes filtering functionality.maildrop receives mail via stdin and delivers in both Maildir and mbox formats....

 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

Mail retrieval agent

A mail retrieval agent is a computer application that retrieves or fetches e-mail from a remote mail server and works with an mail delivery agent to deliver mail to a local or remote email mailbox. MRAs may be external applications by themselves or be built into a bigger application like an MUA...

.

List of message delivery agent software for Unix-like platforms

• binmail, the MDA part of Sendmail
  Sendmail
  Sendmail is a general purpose internetwork email routing facility that supports many kinds of mail-transfer and -delivery methods, including the Simple Mail Transfer Protocol used for email transport over the Internet....
  
  
• deliver
• fdm
  Fdm (e-mail utility)
  fdm is a simple, lightweight replacement for mail fetch, filter and delivery programs such as fetchmail and procmail ....
  
   - A combined mail retrieval agent
  Mail retrieval agent
  A mail retrieval agent is a computer application that retrieves or fetches e-mail from a remote mail server and works with an mail delivery agent to deliver mail to a local or remote email mailbox. MRAs may be external applications by themselves or be built into a bigger application like an MUA...
  
   and mail delivery agent
• maildrop
  Maildrop
  maildrop is a Mail delivery agent used by the Courier Mail Server. The maildrop MDA also includes filtering functionality.maildrop receives mail via stdin and delivers in both Maildir and mbox formats....
  
  
• postdrop
• postfix-maildrop - A mail delivery agent for use with the postfix
  Postfix
  Postfix may refer to:* Suffix * Postfix notation, a way of writing algebraic and other expressions. Also known as reverse Polish notation* Postfix , a mail transfer agent program...
  
   mail transport agent
• procmail
  Procmail
  procmail is a mail delivery agent capable of sorting incoming mail into various directories and filtering out spam messages. Procmail is widely used on Unix-based systems and stable, but no longer maintained; users who wish a maintained program are advised to use an alternative MDA, such as...
  
  
• courier-maildrop
• dovecot
  Dovecot (software)
  Dovecot is an open source IMAP and POP3 server for Linux/UNIX-like systems, written primarily with security in mind. Developed by Timo Sirainen, Dovecot was first released in July 2002...
  
   - A mail server suite that includes a mail delivery agent
• dystill - A filtering MySQL
  MySQL
  MySQL officially, but also commonly "My Sequel") is a relational database management system that runs as a server providing multi-user access to a number of databases. It is named after developer Michael Widenius' daughter, My...
  
   database driven mail delivery agent

See also

• Message transfer agent (MTA)
• Mail retrieval agent
  Mail retrieval agent
  A mail retrieval agent is a computer application that retrieves or fetches e-mail from a remote mail server and works with an mail delivery agent to deliver mail to a local or remote email mailbox. MRAs may be external applications by themselves or be built into a bigger application like an MUA...
  
   (MRA)
• Mail submission agent
  Mail submission agent
  A mail submission agent is a computer program or software agent that receives electronic mail messages from a mail user agent and cooperates with a mail transfer agent for delivery of the mail...
  
   (MSA)
• Mail user agent (MUA) a.k.a. email client
• E-mail agent (infrastructure) (MxA)