Message delivery agent: Difference between revisions
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Within the [[Internet Mail|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 [[Email Mailbox|mailbox]]). | Within the [[Internet Mail|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 [[Email Mailbox|mailbox]]). | ||
Spam filtering usually occurs at the MDA under modern email architectures.<ref>{{cite mailing list |last=Levine |first=John |date=June 10, 2025 |title=SMTP headers in DATA block? |url=https://mailarchive.ietf.org/arch/msg/mailsec/Stxat_WLyMjkleL9g5j6zPFs0vE/ |mailing-list=mailsec |location= |publisher=[[Internet Engineering Task Force]] |access-date=June 10, 2025 |quote="All my experience says that the right place to do mail filtering is the MDA. It has all of the information and has all the options about what to do with the mail. There are MUAs that try to do filtering but that's mostly an historical artifact from a long time ago when MDA filtering didn't happen."}}</ref> | |||
==Implementation== | ==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. | 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. | ||
[[File: | [[File:Diagram of modern email flow.svg|A diagram of the flow of email messages between two participants, Alice and Bob.]] | ||
=== Unix === | === Unix === | ||
Latest revision as of 17:39, 5 November 2025
Template:Short description 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).
Spam filtering usually occurs at the MDA under modern email architectures.[2]
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.
A diagram of the flow of email messages between two participants, Alice and Bob.
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.Script error: No such module "Unsubst".
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.
Unix-like
- 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
- 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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- ↑ Template:IETF RFC, Internet Mail Architecture, D. Crocker (July 2009)
- ↑ Script error: No such module "citation/CS1".
Script error: No such module "Check for unknown parameters".