Complaint feedback loop (FBL)
A provider service that reports back when someone hits 'report spam' on your mail, so you can suppress them right away.
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What it is
A feedback loop is a service a mailbox provider runs for senders: when one of their users hits 'report spam' on your message, they send you a report so you can stop mailing that person. Yahoo, Microsoft, Comcast, and most large providers offer one, usually delivering a copy of the offending message in ARF (Abuse Reporting Format) to an address you nominate. You register per sending domain or IP, and if you use an email service provider they are probably already enrolled, surfacing the result to you as a 'complained' webhook event.
The only correct response is immediate, permanent suppression. Someone who called your mail spam and then receives more of it will complain again, and each repeat costs more than the last. Wire the complaint event straight into your suppression list rather than into a report somebody reads on Monday.
Google's version works differently and surprises everyone. Gmail's feedback loop is aggregate only: it never names the recipient, and it only reports at all once a campaign crosses a minimum volume. To get anything back you have to stamp a Feedback-ID header on outgoing mail (sender-defined fields for campaign, segment, and sender ID), and what returns is a per-campaign complaint rate. So for Gmail you find out which send went wrong, and for everyone else you find out who pressed the button.
Ask AI for it
Set up complaint feedback loops for our sending domain end to end. Register for the Yahoo, Microsoft, and Comcast feedback loops against our sending domain and DKIM signing domain, pointing them at a dedicated mailbox that is parsed automatically rather than read by a person. Parse incoming ARF reports, extract the original recipient from the message or from a header we stamped ourselves, and write it to the suppression list immediately with reason 'complaint'. Add a Feedback-ID header to every bulk message in the form campaign:segment:userbucket:senderid so Gmail's aggregate feedback loop can attribute complaint rates to specific campaigns, and expose those per-campaign rates on the same dashboard as the webhook complaint events. Alert us if a single campaign generates more than 10 complaints in an hour.