What is an Email Feedback Loop (FBL)?
An email feedback loop (FBL) is a programme run by a mailbox provider that sends the sender a report, usually in Abuse Reporting Format (RFC 5965), whenever one of its users marks a message from that sender as spam, so the sender can stop mailing that person.
What a complaint report is
When a recipient clicks “Report spam” or “Junk”, some mailbox providers send the sender a copy of the message wrapped in an Abuse Reporting Format report (ARF, RFC 5965). The report says which message was reported and when, so the sender can stop mailing that person. Subscribing to these reports is called joining a feedback loop.
Who offers them
Feedback loops are provider-specific and each one has its own sign-up. Microsoft (Outlook.com and Hotmail) and Yahoo run per-message programmes that the owner of the sending IPs or domain enrols in. Gmail does not send per-message reports at all. Instead it reports aggregate spam rates in Postmaster Tools, broken down by an identifier the sender puts in a Feedback-ID header — useful for spotting which stream is causing complaints, but not for suppressing an individual address.
What to do with a complaint
Treat a complaint as a permanent unsubscribe from that kind of mail: add the address to your suppression list and never send it marketing again. A complaint rate that stays high is one of the strongest negative reputation signals there is — Gmail and Yahoo ask bulk senders to keep reported spam below 0.3%, and well under 0.1% is a healthier target.
How PostStack handles it
PostStack processes feedback-loop reports for you. A complaint suppresses the recipient and fires an email.complained webhook event, so your application can update its own records. Complaint suppressions are never lifted automatically; see suppressions for how the list works.
Frequently asked questions
Does Gmail have a feedback loop?
Not a per-message one. Gmail reports aggregate spam rates in Postmaster Tools, which it can break down by the identifier a sender puts in the Feedback-ID header. It never tells you which individual address complained.
What should I do when I receive a spam complaint?
Suppress the address from further marketing immediately and treat it like an unsubscribe. Never re-add a complainer automatically. If complaints cluster on one campaign or list source, fix that source.
What spam complaint rate is acceptable?
Gmail and Yahoo ask bulk senders to keep the rate of reported spam below 0.3%, and recommend staying under 0.1%. A sustained rate above that is one of the strongest negative reputation signals.