Anti-SPAM Only Works for Ports 25 and 110

Norton Anti-SPAM will not protect any other than ports 25 and 110.  However, Comcast (XFINITY) customers use ports 995 and 587 to encrypt the email flow between their customers and Comcast email servers.  Why doesn't Norton allow its anti-SPAM ports other than 25 and 110?  In essence, I Norton anti-spam cannot be used by with my ISP connection!