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Glossary · Published 2026-09-29 · AgentiSend team

Feedback loop

Feedback loop: A mailbox provider's notice that a recipient marked the message as spam.

A feedback loop, often shortened FBL, is a mailbox provider's report that someone marked the message as spam. We count it as a complaint and the address joins suppression.

It is not a bounce. The complaint rate is where the ladder reads the count. The report names the recipient; it does not name a new audience to mail.

Related terms

  • Complaint rate — The share of delivered mail that recipients mark as spam, judged by the ladder.
  • Suppression — An address we will not mail. A later send to it is refused.