Feedback loop (email)

A feedback loop (FBL), sometimes called a complaint feedback loop, is an inter-organizational form of feedback by which a mailbox provider (MP) forwards the complaints originating from their users to the sender's organizations. MPs can receive users' complaints by placing report spam buttons on their webmail pages, or in their email client, or via help desks. The message sender's organization, often an email service provider, has to come to an agreement with each MP from which they want to collect users' complaints.

Feedback loops are one of the ways for reporting spam. Whether and how to provide an FBL is a choice of the MP. End users should report abuse at their mailbox provider's reporting hub, so as to also help filtering. As an alternative, competent users may send abuse complaints directly, acting as mailbox providers themselves.

Marketers striving for their mail to be delivered have a twofold advantage: they can remove subscribers that don't want to receive that kind of advertising (listwashing), and they can analyze the complaint rate and hence how their advertising meets market expectations. By unsubscribing users who complain, marketers reduce their overall complaint rate per IP or domain, ensuring that targeted mail is much more likely to reach subscribers who actually want to receive it.

ESPs, when playing the sender's role, are very sensitive to how sending mail on behalf of their customers may affect their reputation. Monitoring the complaint rate is one of the ways they can control what their users are sending.

A weakness of FBL is its relative asynchrony, which can produce glitches. A possibly large time interval sits between ESP subscription to an FBL and a recipient clicking the junk button. The interval between that click and actual deletion of the recipient name from the list is much shorter, but may be noteworthy in the case of huge mailbox providers such as Gmail or AOL. Bulk messages can provide information on how to unsubscribe directly, in the header fields List-Unsubscribe: and List-Unsubscribe-Post:. Besides providing a more direct, better way to unsubscribe, that also allows to tell apart unsubscription from junk reporting (for example, one can report that a message posted to a discussion list is junk, while staying subscribed.)

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Wikipedia