Multiple inbox providers and services offer feedback loops (FBLs) to assist senders in managing complainers and enhancing email deliverability. Key players include major ISPs like Gmail, Yahoo, AOL, and Microsoft, as well as Return Path, which provides a centralized FBL service. Smaller ISPs may offer FBLs, often managed through third-party partnerships. Actively using these FBLs to identify and remove recipients who mark emails as spam is critical for maintaining a positive sender reputation and preventing deliverability issues. Some FBLs have specific requirements, such as email authentication.