From Academic Kids

Sendmail is an open source mail transfer agent (MTA): a computer program for the routing and delivery of email. Its authors released the current version, Sendmail 8.13.4 (, on March 27, 2005. (Note the numbering style used: version 8.13.0 has obsoleted both 8.12.9 and 8.9 and their security vulnerabilities, despite their appearing "higher" in ordinary decimal numeration.)


History and use

A descendant of the original ARPANET delivermail application, Sendmail is a remarkably flexible program, supporting many kinds of mail transfer and delivery including the overwhelmingly popular SMTP. The original version of Sendmail was written by Eric Allman in the early 1980s at UC Berkeley, who had also written delivermail previously. Delivermail was shipped in 1979 with 4.0 and 4.1 BSD. Sendmail was shipped with BSD 4.1c in 1983 (the first BSD version to include TCP/IP).

Sendmail has been widely criticized as slow, overcomplicated, and difficult to maintain by comparison with other MTAs such as Exim, Qmail and Postfix. Nevertheless it remains the most popular MTA on the Internet (albeit not as popular as it once was), a fact almost certainly due in part to its position as the standard MTA under most variants of the Unix operating system. According to one study, as of November 2001 approximately 42% of the publicly reachable mail servers on the Internet were running Sendmail.

Sendmail is often run as the superuser, representing a severe security threat if compromised. This is despite the recommendation since 2001 by its authors that it be run as an unprivileged user. Sendmail version 8.12 (and later) is no longer installed by default as set root id.

Sendmail-8.12 as of September 2001 introduced support for Milter - external mail filtering programs/servers consulted during SMTP session.

In 2003 three serious vulnerabilities were detected and fixed in Sendmail version 8. Two of them were message-oriented and could be exploited even on servers with no direct access from Internet.

In 1988 the Morris worm used vulnerabilities in sendmail and other programs to spread itself.

Sendmail X

The next generation of Sendmail (under development) is called sendmail X ( (previously it was called sendmail 9). It is not an evolution of Sendmail version 8. Although it is purported to be a "complete new design", its design is in fact pretty much an exact copy of the design of Postfix (master becomes MCP, smtpd becomes SMTPS, local becomes LDA, smtp becomes SMTPC, trivial-rewrite becomes AR, and qmgr becomes QMGR). Some have speculated that this, in conjunction with the fact that Postfix exists and is in production use whereas Sendmail X is still being developed, has only accelerated the decline of Sendmail.



The information is based on RELEASE_NOTES file ( from sendmail distribution.


External links


  • sendmail, 3rd Edition by Bryan Costales with Eric Allman, O'Reilly December 2002, ISBN 1-56592-839-3. This is the Sendmail "bible" containing 1232 pages about Sendmail. It is also known as "The Bat Book", because of the picture on its cover.
  • sendmail 8.13 Companion by Bryan Costales, George Jansen, Claus Assmann, Gregory Shapiro, O'Reilly September 2004, ISBN 0-596-00845-7. An excellent companion to popular sendmail, 3rd Edition, this book documents the improvements in V8.13 in parallel with its release.
  • sendmail Cookbook by Craig Hunt, O'Reilly December 2003, ISBN 0-596-00471-0.
  • sendmail Performance Tuning by Nick Christenson, Addison Wesley September 13, 2002, ISBN

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