qmail/MySQL - FreeBSD
If you are running FreeBSD, please use the port (not maintained by me).
Several people reported a bug whereby qmail would hang with this patch. All of these people were using FreeBSD. No one ever reported the bug with any other OS (not even Solaris). Everyone agreed that older versions of the patch worked fine. I was never able to find out the cause of this, although I had some ideas.
The ports people have packaged together known working code. They know what they are doing. Trust them.