High Quality Content by WIKIPEDIA articles! A feedback loop (FBL), sometimes called a complaint feedback loop, is an inter-organizational form of feedback by which an Internet service provider (ISP) forwards the complaints originating from their users to the sender`s organizations. ISPs 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 ISP from which they want to collect users` complaints.