Sendmail is the MTA that takes care of the biggest share of E-mail transportation these days. It was originally written by Eric Allman, who co-founded the Sendmail company.

It was written before the Internet E-mail and SMTP came along. It has support for, well, just about every E-mail transportation method imaginable, past and present - before the standards, you never knew what kind of places you needed to get that mail into. If you knew how to touch the relatively obscure, you could easily get it to transport mail to, say, UUCP or get mail through SMTP-gateway (

These days, such flexibility is no more that much required, but Sendmail is still around, mostly because people no longer need to write (the advent of M4 macro parsing has made Sendmail configuration as easy as writing a few lines and saying "bake it so") - simply, it's much easier to use and configure than it used to - and, ah, it's the standard. =)

These days, the open source (BSD-licensed) Sendmail is at version 8. A commercial version of Sendmail also exists, from Sendmail, inc.

Sendmail is very popular, but other MTAs, such as Postfix and qmail, are getting a tighter stranglehold...

Although Sendmail, Inc. still claims that Sendmail "powers the majority of mail servers on the Internet", others have raised doubts as to whether this remains the case. Dan Bernstein, the author of Qmail, has conducted surveys of mail servers which suggest that between November 1996 and October 2001, the popularity of the Sendmail MTA steadily declined from 80% of all mail servers to 42%. Bernstein's own Qmail stands at 17%, trailing Microsoft's Exchange at 18%.

Why has Sendmail declined thus? After all, it is (as always) free software, and is distributed with the majority of Unix and Linux operating systems. Since a fair majority (at least 65%, according to Bernstein) of mail servers run on Unix systems, this means that a significant number of mail server administrators are choosing to replace a pre-installed Sendmail with another MTA.

I suspect that the chief reasons Sendmail has been rejected include security, manageability, and speed; all three ultimately stem from Sendmail's complexity and history. First, Sendmail has an unfortunate history of security holes. Although current versions are certainly much more secure than old ones, sysadmins have long memories and try to avoid getting burned too many times by the same product. Sendmail also has a reputation for being evil to configure, though this is ameliorated greatly by M4. Finally, and perhaps most importantly for large sites, Sendmail is quite heavy compared to many other MTAs. Lighter ones such as Postfix or Qmail can handle higher volumes of mail using less computing power -- and thus costing less money.

Dan Bernstein's surveys are available at As Bernstein is the author of a rival (albeit free) MTA, you may wish to take them with a grain of salt. However, they do seem to jibe well with my experience -- and, I'll admit, with my own biases: if you're setting up a mail server, I'd recommend you look into Postfix and Qmail in particular before considering Sendmail too strongly.

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