Symantec 11105111 - SYM MAIL SEC SMTP 5.0 SMS PORT MEDIA CD EN User Manual page 123

8 If desired, in the None of these terms box, type the terms to be used to
identify that a message is not spam.
If a term is in the Not field and a message is sent that has all of the blocked
terms (AND/OR portion of rule) but also has a Not term, the message will
not be in violation of the rule. (It will not be considered spam.)
9 Click Save.
Setting your antispam policy
Blocking by custom spam rules
123