MTA
===

MTA is an acronym for _M_ail _T_ransport _A_gent. It is the software that works
behind the scenes to transport E-Mail messages from one computer to another.
MUAs (such as mutt, thunderbird, sylpheed, evolution, kmail) hand off newly
sent messages to an MTA. MTAs talk to other MTAs, and either deliver mail
locally or hand it off for delivery to an <MDA/LDA> [MTA.txt] if it was
destined to the local system.

MTA is a generic term and usually refers to one of these popular software
packages:

 * Postfix [http://www.postfix.org/] is Wietse Venema's secure, fast and
   flexible mailer. Default on SUSE Linux and NetBSD.
 * Exim [http://www.exim.org/] is Philip Hazel's flexible mailer. Default on
   Debian GNU/Linux.
 * Sendmail [http://www.sendmail.org/] the original BSD mailer. Default on
   FreeBSD; a Sun spinoff is used on Solaris.
 * Courier [http://www.courier-mta.org/] was inspired by qmail, but intends to
   do things right.
 * qmail [http://cr.yp.to/qmail.html] is an obsolete and unmaintained server.
   Its POP3 part can be taken over by Dovecot. Qmail started off boasting about
   speed and security in the mid-1990s, but has lots of unfixed bugs (this
   document includes patches where known),
   [http://home.pages.de/~mandree/qmail-bugs.html] among them security bugs
   that remain unfixed, and the security guarantee (500 USD) denied. If you
   really intend to continue using it, read Dave Sill's Life with qmail
   [http://www.lifewithqmail.org/] which contains instructions to work around
   some of qmail's security issues.
 * HALON [https://halon.io/] is a commercial MTA, which supports Dovecot Auth
   and LMTP. It's based on FreeBSD with anti-spam/virus, DKIM, DMARC, DANE,
   etc.

Some people also subsume mail fetching utilities under the MTA category, among
them:

 * fetchmail [http://www.fetchmail.info/] a fast mail retriever for the POP2,
   POP3/KPOP/SDPS, IMAP2/IMAP4, ODMR and ETRN protocols, SSL and Kerberos
   capable. It forwards the retrieved messages to SMTP/ESMTP, LMTP servers or
   into an <LDA.txt>. Developed out of Carl Harris's popclient by Eric S.
   Raymond. Fetchmail is now maintained by <MatthiasAndree.txt> and Rob F.
   Funk.
 * getmail [http://pyropus.ca/software/getmail/] a POP3/SDPS and IMAP4 (with
   SSL) enabled mail retrieval utility written in Python. Developed by Chales
   Cazabon.

These mail fetching utilities can be used to store mail for later retrieval by
dovecot.

 Contrast this to the <message delivery agent (MDA)> [MDA.txt], sometimes
called local delivery agent (LDA).

(This file was created from the wiki on 2019-06-19 12:42)
