Feedback loop (FBL)
Also called: FBL, Complaint feedback loop, CFL
A feedback loop is a service through which a mailbox provider tells a sender when recipients mark their email as spam, so the sender can stop emailing them.
Operational recommendations for feedback loops are in RFC 6449 (IETF). Yahoo says an active Complaint Feedback Loop is needed for all DKIM domains (Yahoo). Gmail reports spam rates in aggregate through Postmaster Tools rather than per message.
How it affects cold email
Without a feedback loop you only see complaints indirectly, as worse placement. With one, you can suppress each person who complained, which is the least you owe them.
How Inboxed handles it
- Inboxed adds a
Feedback-IDheader identifying the campaign and workspace to every campaign email. Complaints reported through the report abuse page are added to your suppression list as complaints. Signing up for a provider’s feedback loop with your own domain is up to you.
Related terms
Sources
Sources checked on 8 November 2026. Rules change, so check the source before you rely on a detail.
- RFC 6449: Complaint Feedback Loop Operational Recommendations · IETF
- Sender Best Practices · Yahoo Sender Hub
- Email sender guidelines · Google, Gmail Help
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