Beginning last week, my XServe again began rebooting, about 2 times a day. We spent many hours trying to narrow it down. Finally, we shutdown qmail and replaced it with postfix. We've been up for 42 hours now.
A little sad, cuz I like qmail, but the reboots were obviously Not a Good Thing. What worries me is how many other unix programs that compile fine and seemingly run okay are going to fail to the point of hanging the system.
But really I'm quite happy. Stability makes me giddy. :-)