2. Preliminary installation steps

Before delving into the installation and configuration of all the mail-handling software, we will take a brief look at the operating system that will host it.

As usual, my choice goes to OpenBSD for its proven security, reliability and ease of use. Needless to say, all these features are essential for a system that will have to handle a large volume of email traffic while still making life hard for spammers and malicious users.

We won't cover the installation procedure here, which is documented in full detail on the OpenBSD web site. Just a couple of notes:

• while partitioning the hard drive, bear in mind that we will configure Postfix to use virtual domains and, consequently, it will store all users' mail folders in a single directory (/var/vmail). Therefore, it is recommended to assign a (large) dedicated slice to this filesystem, in order to prevent mails from filling up any critical filesystem, should quotas fail;
• the only file sets we will need to install are those marked as "required" on the documentation, i.e. bsd (the kernel), baseXX.tgz (the base system), and etcXX.tgz (the configuration files in /etc) plus compXX.tgz (the C compiler), since we will have to install some ports not available as precompiled packages for licensing reasons. Note: since leaving a compiler on a publicly accessible server is a definite security risk, it is recommended that you remove the compiler when the installation is over or that you compile on another machine.

Since version 5.4, OpenBSD doesn't start inetd(8) by default, so there are no unnecessary daemons to prevent from running; to modify the server network configuration, please refer to the appropriate chapter in the previous document about redundant firewalls or to the Networking FAQ.