I initially started using OpenBSD as a home firewall because of it's reputation for security. Since that's the OS I'm used to, and because of the good rep, I went with OpenBSD for my mail server as well.

OpenBSD setup is fairly straightforward. I recommend either buying the CDs, or at least downloading all of the files in advance and storing them on a local server. Should you decide you want to start from scratch, nothing's more painful than having to wait through another download of all the packages.

Some caveats I've run into:

• Pay attention to your partitioning scheme and how much storage you give /. Dont forget that everything else you dont partition for ends up under / and that root is not under /home. Case in point - I set up a machine with seperate (and ample) partitions for /home, /var, /usr, and even /tmp, but didn't leave so much for /. Since I didn't create a seperate partition for /root, I was always running out of space when doing quick application installs as root (of course, that's a good reason to not do compiles from your home directory as well).
• Be aware of domain naming issues. My setup has several machines behind a Firewall/NAT box. Each machine has a subdomain name (postoffice.mynetwork.com, cartman.mynetwork.com, etc.). Having your box represent a root domain while not actually being named a root domain can cause access troubles. Some applications may allow a client on postoffice.mynetwork.com, but may barf if the client is just coming from mynetwork.com, etc. MySQL? permissions seem to be a specific gotcha in this case.
• Even though I was led down the path early on of "compile everything from the ports tree", using packages can be a lifesaver. Especially when it comes to setting up PHP. I spent hours trying to get PHP to compile with all of the required mods for some of the apps I wanted to use with no success. In the end, it was 5 minutes of pkg_add commands that saved the day.

-- ChrisWeiss - 11 Feb 2005