How do FBLs work?

Feedback Loops (FBLs) are systems that notify senders when recipients mark their messages as spam. When a user clicks the spam button, the mailbox provider generates a report and sends it to the sender's registered FBL address.

The report typically includes the recipient's email address, allowing the sender to suppress that address from future mailings. Some FBLs anonymize or hash the recipient address for privacy protection.

FBLs require registration. Senders must sign up with each provider offering the service and verify ownership of their sending domains or IPs.

FBLs are like complaint forms that the harbor authority forwards to shipping companies. When merchants report problems with your cargo, you receive the feedback to improve your operations and avoid repeat offenses.