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SMTP Server
Options for Linux
Quite a few SMTP servers are available for
Linux. The four most popular are: Sendmail The mail server with the largest installed base, and the one that
ships with most Linux distributions, is sendmail. This package is large and
powerful, and many programs assume that sendmail is available, so other
packages usually include a binary called sendmail to maintain
compatibility. Sendmail uses a complex configuration file format, which is one
of the reasons alternatives have been growing in popularity. The main sendmail
Web site is http://www.sendmail.org . Exim Exim is a mail server that was designed to use a simpler
configuration file format than sendmail, and to support various sophisticated
filtering operations on mail. It's the favored mail server with Debian and its
derivative distributions. The main Exim Web site is
mail servers, meaning that they perform most tasks in a single large program. Postfix
was designed in a modular way, meaning that
tasks are broken up and handled by smaller programs. This has certain security
and speed benefits. These and Postfix's simpler configuration files are its
main advantages over sendmail. Linux Mandrake ships with Postfix as the default
mail server. You can learn more about Postfix at
security and performance in mind. The qmail configuration file is simpler than
that of sendmail, but the program is less compatible with sendmail than either
Exim or Postfix, so it's a bit more difficult to replace sendmail with qmail. Although
it's turned up as the second most popular UNIX and Linux server in surveys of
Internet mail servers, qmail isn't the default mail server for any Linux
distribution, so I don't discuss it at length in this chapter. The main qmail
Web site is http://www.qmail.org .Although these are the most popular Linux
mail servers, there are others, such as Smail (
"big four" account for most of the discussion of mail servers in the
Linux community. All four of these programs are very powerful and able to
handle the mail needs for most domainseven very large ones.Particularly if you're new to mail server
administration, you're probably best off using whatever SMTP server shipped
with your distribution. Many distributions now include multiple SMTP server packages.
The default is probably the best choice.If you have specific needs, and particularly
if you have exotic needs, you may want to investigate the capacity of various
mail servers to meet those needs. If necessary, you can replace your standard
mail server with another one. Because of sendmail's popularity, this usually
means replacing sendmail with another server. Exim and Postfix usually work
well as "drop-in" sendmail replacements. Although the configuration
files are completely different, programs that call sendmail directly usually
work well with Exim and Postfix, and the mail queue format for these two
programs defaults to the same format that sendmail usesnamely, the mbox
format, in which all mail in a single mail "folder" is stored in a
single file. Replacing sendmail with qmail is usually a bit more involved,
because qmail defaults to a different mail file format (the maildir format,
which uses a directory in which messages are stored as individual files), so
you may need to change the standard qmail configuration or replace your mail
programs (including any pull mail servers you want to run, as discussed in
