I just wanted to mention something about spamassassin for liquidcherry:

If you have the filtering system turned on that deletes all mail that has the spamheader marked as YES then you could loose all your email because of something that happens in spamassassin.

If you find that spamassassin all of a sudden marks all email as spam it has to do with the two following files

bayes_toks
bayes_seen

which reside in your domain root/.spamassassin folder

you will see that at least one of the files has grown in size to be more than 500 KB.

The way around the problem is to remove the two files and in the user_prefs file in the same directory add the following somewhere.

# Enable Bayes auto-learning
use_bayes 0
autolearn 0

This will stop spamassassin from ever deleting all your mail again.

Hope this helps.