I have a client running a plesk/qmail hosting service who is having some
trouble with getting their shared ip listed on spamhaus. I believe they
are already running SA in some capacity. I am also looking into various
solutions to suggest to them, possibly including mailscanner if it can
be integrated into the plesk environment. For now I would like to try
and determine why they keep getting listed on spamhaus. Can anyone
suggest some tips or a starting point to determine why they might keep
getting listed?

I will be reviewing their maillogs to see if there is any mass mailings
going out from any of their hosted domains on the shared ip to start.