I have a situation where we suddenly got 1000's of emails in the outgoing queue that are spam. The 'from' address is a hotmail account, the sender is (I assume webmail interface), and they caused me a big problem.

The only issue is I cannot see from the log files which authenticated user sent them. The server is definitely not an open relay.

How can I find out what user sent the emails?

Also, is it possible as we did with our other mail server to limit outgoing emails per day per account so this cannot happen? All I can find is a single storage quota. Nothing re traffic quotas.