Glossary

FBL (Feedback Loop)

FBL (Feedback Loop)

A Feedback Loop (FBL) is a service offered by mailbox providers that reports when a user marks a message as spam. Senders use FBLs to suppress future sends to complaining recipients and improve overall list hygiene and deliverability. Not all providers leverage FBLs; Gmail and iCloud, for example, do not share FBL data with senders. 

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