Though the question was partially answered in another post here today, but I have a question. I just checked my email stats in whm, and it has a list of over 4600 errors, which are bounced emails. Does this mean that someone is using my server for spam? If so, how do I know for sure? And, is there a way to stop it if they are? Also, I'd love any email server settings advice to help stop this problem (if there is a problem in the first place). Thanks guys.
4600 would not be a lot of spam if someone was sending out. Chances are it is email that is spam that has a bogus domain name to a user on your system that does not exist and your mailserver is throwing an error saying it can't find the domain.
it also could be your server getting in mail and first checking if it can reverse the domain on the email.