Spam complaint
A recipient's report that a message is unwanted, usually made with the mail client's spam button, which providers count against the sender.
What it means
M3AAWG describes the spam button in a webmail interface or mail client as the most frequent way recipients complain, alongside tickets, calls and emails to a provider's abuse desk or to the sender. RFC 6449 defines spam, for feedback loops, as any message the recipient chooses to complain about, regardless of the intent of its author or sender. A newsletter someone forgot signing up for counts the same as unsolicited mail.
Complaints feed the sender's reputation and the complaint rate that Gmail and Yahoo cap at 0.3%. Feedback loops return them to the sender so the complainant can be removed; some providers redact the recipient's address in those reports, as RFC 6449 notes.
Spamhaus advises using feedback-loop complaints both to remove every complainant and as an early warning about the program that produced them.
Related terms
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Sources
What this definition rests on. The wording is ours; the facts are theirs.
All 432 terms in the glossaryThe wiki: blocklists and bounce codes