The FreeBSD 'zine
February 2000 : Qmail

An introduction to qmail
By Gavin Cameron <[email protected]>

This is the first of five articles on qmail that will appear over the next couple of months. The topics I will cover are

  • qmail introduction
  • installing and configuring qmail
  • virtual domains and qmail
  • ezmlm - qmail's mailing list manager
  • anti spam and qmail
The qmail WWW page immodestly touts qmail to be a modern replacement for sendmail but the purpose of this series of articles is not to bash sendmail, postfix or any other MTA (Mail Transport Agent) but rather to document my observations, trials and tribulations during my implementation of qmail on a number of production servers.

I'm not going to rehash a heap of qmail documentation from various WWW pages, instead I'll point you at a number of pages describing qmail, its functionaility and various add-ons.

A little history

qmail was written by Dan Berstein from University of Illinois at Chicago to fulfill the following requirements
  • Security
  • Reliability
  • Efficency
  • Simplicity
  • Replacement for sendmail
Beta testing began in January 1996, gamma testing in August 1996 and version 1.00 was released in February 1997. Since that time a number of small changes has seen the qmail version number creep up to 1.03. Version 2 is currently under construction.

The qmail installation package comes with a number of BLURB pages that my paraphrasing won't do justice to so I'll just list them here for your viewing pleasure.

That's all well and good if you beleive marketing hype and hopefully my next couple of articles will sort the chaff from the wheat.

Is qmail secure?

Dan Bernstein offered a $500 reward to the first person to publish a verifiable security hole in the latest version of qmail: for example, a way for a user to exploit qmail to take over another account.

The offer still stands.

You can find the qmail security guarantee here.

The structure of qmail

qmail consists of a number of small easily verifiable (securitywise) programs that perform well defined tasks. Smaller programs mean that a security flaw in one program is confined to just that component at the expense of increased overhead because of additional fork()s and exec()s required to start the qmail components.

The following links show how all these smaller components fit together deliver E-mail.

The biggest hurdle

When you install qmail you need to choose whether to use the standard mbox file format or change to qmail Maildirs. A Maildir is a lock-free mailbox standard which is reliable over NFS.

The main drawback with moving to Maidirs is MUA support for Maildirs. Mutt comes standard with Maildir support and Pine (well its IMAP server) can be patched to use maildirs.

POP3 support comes standard with qmail and the Courier-IMAP package gives you IMAP functionality.

Next time

In my next article I'll be taking you through the installation of qmail, tcpserver and the daemontools packages that all go together to produce a highly reliable mail server. Until then, read the URLs listed in this article in preparation for installing qmail.

URLs from this article

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