Explanation/Reference:
A: Spamblocker requires DNS to be configured on your XTM device
B: If you use spamBlocker with the POP3 proxy, you have only two actions to choose from: Add Subject Tag and Allow. Allow lets spam email messages go through the Firebox without a tag.
D: The Firebox might sometimes identify a message as spam when it is not spam. If you know the address of the sender, you can configure the Firebox with an exception that tells it not to examine messages from that source address or domain.
Reference: Fireware Basics, Courseware: WatchGuard System Manager 10, page 138