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Security Portal: Kurt's Closet: Postfix - the Sendmail replacement

Sep 15, 1999, 14:10 (4 Talkback[s])
(Other stories by Kurt Seifried)

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"In all fairness Sendmail is a damn good MTA (Mail Transfer Agent), Eric Allman originally wrote it with one main goal in mind: the mail must get through. Unfortunately, when Sendmail was originally written security wasn't a major concern on the Internet and it shows. Sendmail runs almost exclusively as the root user on most systems, meaning any flaws are potentially very serious. In addition to this Sendmail isn't very good at handling high loads. New mailers, such as Postfix, Zmailer, and Qmail are several times faster then Sendmail on the same hardware. Until recently most of the alternative mailers to Sendmail were not drop-in replacements, to replace Sendmail was a painful task, and the new software typically behaved differently then Sendmail. Postfix was designed from the start to address all these problems."

"Postfix does not run exclusively as root, instead a master program (called "master") runs as root and spawns off processes to handle incoming, outgoing and local mail delivery as needed. Using a series of modular components, each task is handled by a separate program (which makes auditing it easier), for example outgoing email is dumped into the queue directory by your software, where "pickup" gets it and hands it to "cleanup", which hands it to "trivial-rewrite" which handles the headers, and finally is given to "smtp" if bound for a foreign system. Postfix is also much easier to setup for a chroot'ed environment than Sendmail is, simply make a few edits to the file (typically in /etc/postfix) and Postfix will run chroot'ed in its defined queue directory (usually /var/spool/postfix). It is also possible to set process limits for individual portions of postfix, again in the file."

"As stated before, replacing Sendmail with another MTA used to be a very painful task, many mailers approached the "problems" in Sendmail by doing things quite differently and require a pretty extensive overhaul of the mail system, and a very different set of configuration files. With Postfix you can use most of your existing configuration files (such as access, aliases, virtusertable, etc.) simply by defining them appropriately in the file. In addition to this Postfix behaves like Sendmail, you can invoke it using "sendmail", get a listing of the mailq with "mailq", feed it pretty much the same options and so forth. I find a typical Postfix conversion takes around 10 minutes for most sites..."

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