Mail not Addressed to You is Likely Spam

There is hardly an unsolicited mass email message that has your email address in the To: or the Cc: field.

This is why you can set up a filter that

• moves all incoming messages that do not carry any of your email addresses in either the To: or Cc: field to the "Probably Spam" folder.

Of course, you should have filters that catch all mail from mailing lists before the not-addressed-to-me filter triggers.