qmail.org has many mirrors. To let people know which mirrors are well-maintained, I check every mirror every day using a script. The script fetches http://qmail.example.com/timestamp.html, and compares it to the one on mirror.qmail.org. If that file is unavailable for any reason, or is badly formatted, a note is inserted into the listing of mirrors. Also, if the mirror has been unavailable in the past two weeks, and they've been unavailable for more than four times in the past several months, they get a red bar next to their name, indicating the number of days of outage.
If there is a note, then the script has also sent email to the responsible person at the mirroring site. I call this the Auto-Annoy feature. If that email bounces (yes, you'd think that qmail mirror admins would have well-administered email systems, but no), then that adds two days to the red bar.
That's how it currently works. In the future, I'm going to modify it to also check each site to see if the site also responds to qmail.org as the name of the server. If it does, then the site will be added into a round-robin record for qmail.org.
Here's the mirroring software itself.