A spam filter should act when one account sends several similar mails to numberous accounts unrelated to the sender. A spam filter should not act when a hot to

A spam filter should act when one account sends several similar mails to numberous accounts unrelated to the sender. A spam filter should not act when a hot topic is `trending' -- being send around from multiple accounts mostly to accounts related to them (with existing history of communication). A spam filter acting on mere global volume of a keyword is a prime example of solution more troublesome than the original problem itself.