FBL

FBL is short for "feedback loop," which is a way to communicate feedback between email users and email senders' organizations when complaining about email abuse (spam). The loop refers to the connection between the sender, the message sent, the recipient, and the feedback report sent to the sender.

As the Internet advanced in the 1990s and 2000s, "spamming" became a common method for sending unsolicited messages to many people. The spam may be sent for various purposes, most often as part of a commercial advertising effort or a nefarious purpose, such as transmitting a computer virus. Spamming frustrated many email users, leading to the development of the FBL to help report spam.

There are various ways for a user to initiate feedback in the FBL, but the most common is a spam reporting button in an email client or on a webmail page. When a user receives a message that he considers spammy, he clicks the button to report the spam, which notifies the mailbox provider (MP) or Internet service provider (ISP).

The MP or ISP then sends a report of the complaint, most often in ARF format, to the email's sender. However, the email sender must be subscribed to the feedback loop to receive the feedback.

Even when email users report spam, they probably still won't know what a feedback loop is. The term is not very common, mostly known only among mail providers and mass email marketing senders that subscribe to the feedback loop.