Symantec Mail Security for Microsoft Exchange is installed on an Exchange server. The Premium AntiSpam feature, the AntiSpam Heuristics engine, or Real-time Blacklists have been enabled. Spam, is still received and the spam statistics show zero spam detections.
Email is through a POP3 server.
Symantec Premium AntiSpam and the AntiSpam Heuristic engine scans only SMTP traffic.
If POP3 is used to receive email from outside of an organization, Symantec Mail Security for Microsoft Exchange cannot detect spam in that email.