Quick question as I have been searching all over for a solution to my
problem.

I'm running Exchange 2007 and have a problem where user accounts are
getting compromised and being used to send spam out and make us end up
on blacklists.

Unfortunately being a College we have ~30,000 accounts and a majority
of them being students makes it difficult to manage and maintain. We
have complex passwords in place but that doesn't appear to help us.

Is there any way to:
1. Spamcheck outgoing mail messages.
2. Limit the number of outbound messages per use (some form of
throttling)

or do you have any suggestions to my problem?