I've been having reliability problems with a flaky drive on my primary desktop box, which happens to also be my primary mail server for my personal domain. Unfortunately, when that machine goes down, so does all the email for everyone in my domain. I can live with that for a few hours, but this has happened now for the better part of three days, which is unacceptable. I therefore set about to move my SMTP server off my desktop box (running Ubuntu 11.04) and onto my firewall box (running CentOS 4.9). Nothing much ever changes on the firewall, and it runs on server-class hardware (an HP ProLiant), so it should be a far more reliable platform.