Hello!,
There are many possibilities to solve your needs, maybe run an AntiSpam to protect Internet from your users (and prevent to be blacklisted), "scrollout f1" is a great antispam solution, you can install it or I can help you :)
In the other hand, you can install SpamAssassin (or other antispam) on same server, again, you can install it or I can help you :)
Can you explain me your needs so I can propose a solution?
Thank you!