Why do I receive messages whose subject starts with [SPAM]?

The UVSC E-Mail Firewall has three levels with which to handle spam. First, it blocks messages that it is 100% sure are spam. Second, it quarantines messages that it is almost positive are spam. Third, it tags (by adding [SPAM] to the subject) messages that is thinks might be spam, but isn't very confident. To ensure that future spam messages are blocked or quarantined, please send all spam (including those with [SPAM] in the subject) to MAILADM. We use these messages to teach the system what is spam and what is not.