/ Glossary — Reputation & Bounces
What is a feedback loop?
The channel by which a mailbox provider tells you when a recipient marks your mail as spam — so you can stop mailing them before they sink your reputation. Here's how it works.
/ Definition
A feedback loop, or FBL, is an arrangement by which a mailbox provider notifies a sender each time one of their recipients marks a message as spam. It's the channel that turns an invisible complaint into actionable information: without an FBL, you'd have no way of knowing which recipients hit the spam button, and therefore no way to stop mailing them.
FBLs are essential because complaint rate is one of the most damaging signals in email, and the only way to manage it is to know who complained and suppress them immediately. Most major providers offer feedback loops, and quality sending platforms process them automatically, adding complainers to a suppression list the moment a complaint arrives.
/ In practice
How feedback loops work
When a recipient marks your mail as spam at a provider that offers an FBL, the provider sends a report back to the sender — typically to a registered address, in a standard format identifying the message that was complained about. The sender's system reads the report and acts on it, almost always by suppressing the complaining address so it's never mailed again. The mechanics vary by provider: some require registration and authentication to receive the reports, while others, like Gmail, work differently, surfacing aggregate complaint data through Postmaster Tools rather than per-message reports.
Why processing them matters
An FBL is only useful if you act on it, and act fast. A recipient who complained once and keeps receiving your mail will complain again, driving up your complaint rate and damaging your reputation with every send. Automatic, immediate suppression of complainers is the baseline competent handling — a feedback loop whose reports pile up unprocessed is worse than none, because it means complaints are happening and being ignored. This is why FBL processing belongs in the sending infrastructure, not in a human's inbox.
/ Which providers offer FBLs
The patchwork of provider support
Feedback loop support varies by provider, and the differences shape how you process complaints. Several large providers and many smaller ones offer traditional FBLs that send a per-message report when a recipient complains, usually after you register and prove control of your sending domain or IP. Gmail is the notable exception: it doesn't provide per-message complaint reports, instead exposing an aggregate spam-rate figure through Postmaster Tools, so monitoring Gmail complaints means watching that dashboard rather than processing individual reports. Yahoo and Microsoft have their own mechanisms. The practical consequence is that complete complaint visibility requires covering several different systems at once — registering for the FBLs that exist, and watching the dashboards for the providers that don't offer them. This patchwork is one reason complaint handling is easy to do partially and hard to do completely, and why it tends to be a sending-platform responsibility rather than something done by hand.
/ Related terms
A complaint you can't see is a complaint you can't stop. We process every FBL automatically.
We register and process feedback loops across providers, suppressing complainers the instant they appear. Bring us your sending and we'll close the loop.
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