What is Spam complaint rate?
Spam complaint rate is the share of delivered messages that recipients marked as spam.
Also called: spam rate, complaint rate.
When a recipient clicks Report spam, their mailbox provider records a complaint against the sender. Providers count complaints against messages delivered to their users, and the resulting rate is one of the strongest inputs to sender reputation.
Google's sender guidelines ask bulk senders to Gmail, those sending more than 5,000 messages a day, to keep their spam rate below 0.30%. That is a ceiling, not a target: well-run programmes sit far below it.
Cold email is more exposed to complaints than permission-based mail because no one asked for it. Three habits keep the rate down: target narrowly so the message is relevant, make opting out easy (a plain reply option and, for marketing mail, one-click unsubscribe), and stop after a short sequence rather than mailing indefinitely.
Complaints cannot be fully predicted from content, but bait subject lines and spam-filter vocabulary make them likelier; the spam word checker and subject line grader flag both.