What is an email feedback loop?
Also called: FBL, complaint feedback loop
A feedback loop is a service a mailbox provider runs to tell a registered sender when its recipients mark a message as spam. Complaints arrive as reports, usually in the Abuse Reporting Format (ARF), so the sender can suppress the complainer and spot the campaign or list causing trouble.
Yahoo runs a complaint feedback loop keyed to DKIM domains, and Microsoft runs the Junk Mail Reporting Program. Gmail's version is different: it gives large senders aggregate complaint data by campaign through Postmaster Tools, using a Feedback-ID header, rather than per-message reports.
Every complaint should go straight onto your suppression list. Mailing someone again after they reported you is how a complaint rate climbs.
Most sending platforms register for the feedback loops on your behalf. If you send from your own infrastructure, registering is your job.
Read the reports for patterns, not just addresses. Complaints clustered on one campaign point at the content or the audience; complaints clustered on one list source point at how that list was built.
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By SimpleVerifier Team · Last reviewed 2026-10-13 · All 50 glossary terms