Picking the Right Mail Server

As with many types of servers, Linux systems offer a wide variety of SMTP servers. The most popular Linux mail servers are all very powerful programs that are capable of handling large domains' mail needs, when paired with sufficiently powerful hardware. The most popular servers are:

Sendmail This server, headquartered at http://www.sendmail.org, has long dominated Internet mail delivery. Daniel Bernstein, the author of the competing qmail software, conducts periodic surveys of SMTP servers. The most recent of these was conducted in September and October of 2001, and it is reported at http://cr.yp.to/surveys.html. This survey shows sendmail running on 42 percent of systems—the most of any server, by a wide margin. Sendmail has earned a reputation for a difficult-to-master configuration file format. Fortunately, tools to create a configuration file from a simpler file are common. In the 1990s, sendmail suffered from a series of serious security bugs, but such problems have been less common since the late 1990s. Red Hat and Slackware both use sendmail as their default mail server.

Postfix The Mandrake and SuSE distributions both use this server as their default mail server. Although it was used on only 15 of 958 servers in Bernstein's 2001 survey, its presence as the default on two major Linux distributions makes it a very important server in the Linux world. Postfix uses a series of small programs to handle mail delivery tasks, as opposed to the monolithic approach used by sendmail. The result is greater speed and, at least in theory, less chance of serious security flaws. (In practice, Postfix has a good security record.) Its configuration is much easier to handle than is sendmail's. You can learn more at http://www.postfix.org.

Exim This mail server, described at http://www.exim.org, is the default for Debian. Bernstein's survey shows it in use on 14 of 958 servers. Like sendmail, Exim uses a monolithic design, but Exim's configuration file is much more intelligible. This server includes extensive pattern-matching tools that are very useful in fighting spam.

qmail This server is the second most popular Unix mail server in Bernstein's survey, with 167 of 958 server computers running the program. Despite this popularity on the Internet, qmail isn't the default server for any major Linux distribution, perhaps because its license terms are peculiar—they don't permit distribution of binaries except under limited conditions. Like Postfix, qmail uses a modular design that emphasizes speed and security. Check http://www.qmail.org for more information.

Tip If you want to run qmail, you can find links to binaries, including RPMs and Debian packages for many popular distributions, on the qmail web site. You needn't compile and install the software from source code unless perhaps you're running an unusually new, old, or exotic distribution.

For light duty—say, for a small business or personal mail server—any of these programs will work quite well. For such cases, I recommend sticking with whatever software is the standard for your distribution. Using the default server means you'll be less likely to run into strange configuration problems or incompatibilities. For larger installations or if you need advanced features, you may want to investigate alternatives to your distribution's default server more closely. You may find particular features, such as Exim's pattern-matching tools or the modular design of Postfix and qmail, appealing. All of these servers are capable of handling large or busy domains, although sendmail may require speedier hardware than the others to handle a given volume of mail. For small sites, even sendmail won't stress any but the weakest computers.

The following sections describe the configuration of sendmail, Postfix, and Exim in more detail. I've omitted qmail because it's not the default server for any major distribution, but it's certainly worth considering if you want to change your mail server.

Team LIB

Team LiB

^ previous

0 0

Post a comment