ISP Feedback Loops/Complaint Feedback Loops (FBL) is a process which allows mailbox providers a method to forward user generated complaints back to the sender or Email Service Provider.  In order to receive the FBLs, the senders or Email Service Providers must first subscribe/register with the organizations which offers it.  It is common best practice to treat/honor the FBLs as a user requested unsubscribe.

Current list of ISPs and organizations offering Feedback Loops are listed- List URL and reference links to ISPs and Organizations supporting Feedback Loops

 AOL
 Bluetie/Excite
 Comcast
 Cox
 Fastmail
 Hotmail
 Mail.ru
 OpenSRS/Tucows
 Rackspace (formerly Mailtrust)
 RoadRunner/Time Warner Cable
 Synacor
 Terra
 USA.NET
 United Online/Juno/Netzero 
 Yahoo!
 Zoho.com