Feedback loop
A service in which a mailbox provider reports back to a sender each time one of its recipients marks a message as spam, so the complainant can be removed.
What it means
RFC 6449 codifies how complaint feedback loops work: the mailbox provider collects spam reports from its users and forwards them, in the Abuse Reporting Format, to the sender or network that signed up. M3AAWG defines an FBL as a system that gives qualified senders copies of the messages their recipients reported as spam, so they can find and fix the cause.
Each provider runs its own. Yahoo's Complaint Feedback Loop is domain-based and requires DKIM signing. Microsoft's JMRP is part of SNDS. Gmail's Feedback Loop reports spam rates by campaign identifier in Postmaster Tools, not individual messages. Apple says iCloud Mail offers none, and M3AAWG's 2019 position paper notes that hosted business mail at Microsoft and Google had no FBL.
Every complainant in a feedback report should be suppressed, as Spamhaus advises.
Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 6449: Complaint feedback loop operational recommendationsrfc-editor.org
- M3AAWG Sender Best Common Practices, version 4.0 (August 2026)m3aawg.org
- Yahoo Sender Hub: Complaint Feedback Loopsenders.yahooinc.com
- Gmail Help: Feedback Loopsupport.google.com
- Apple Support: Postmaster information for iCloud Mailsupport.apple.com
- M3AAWG Position on Selling Email Address Lists (June 2019)m3aawg.org
All 432 terms in the glossaryThe wiki: blocklists and bounce codes