There's this myth that automated spam detection is hard because spammers are all very clever masters of disguise.

No. Spammers are stupid as a shoe. They have dog shit for brains.

Automated spam detection is hard because the line between spam and "legitimate" marketing activity is a fiction.

@danslimmon There is no "legitimate marketing activity" in email. Any mail that's sent in mass of a commercial nature is spam.
@dalias
Hard to differentiate though. When Oracle's billing department produces mails that confuse spam filters..
@danslimmon