This list was originally present the wiki for this mailserver repository wiki page. I've created a gist with it as it is something that can be useful per se and I'd like to keep a copy of it.
A Feedback Loop (FBL) is a system by which an Internet Service Provider provides the sender a copy of the message that one of their subscribers has reported as spam — usually by hitting a “report spam” button in that ISP’s mail interface.
ISPs offer feedback loops to qualified senders, so the senders can identify subscribers who no longer want to receive similar mail and/or any problems originating from their networks, such as virus-infected spam-producing machines.
This page summarizes the information about FBL signup pages, whitelist pages, and postmaster pages of most popular ISPs around the world.
| ISP | Info | Postmaster Page |
|---|---|---|
| AOL | Yahooinc FBL | Yahoo Sender Hub |
| AT&T | does not provide | AT&T postmaster |
| Comcast | Validity | Comcast postmaster |
| Earthlink | Earthlink FBL signup | does not provide |
| Excite (Bluetie) | Validity | Excite postmaster |
| FastMail | Validity | does not provide |
| Gmail | support.google.com) | Gmail postmaster |
| Hotmail | Hotmail FBL signup | Hotmail postmaster |
| Mail.ru | Mail.ru FBL signup | Mail.ru postmaster |
| Outblaze | Outblaze FBL signup | does not provide |
| Rackspace | Validity | Rackspace postmaster |
| Synacor | Validity | does not provide |
| Tucows | Tucows FBL signup | does not provide |
| UnitedOnline (NetZero/Juno) | does not provide | UnitedOnline postmaster |
| USA.net | USA.net FBL signup | USA.net postmaster |
| Verizon | does not provide | does not provide |
| XS4ALL | XS4ALL FBL signup | does not provide |
| Yahoo! | Yahoo! FBL signup | Yahoo! postmaster |
| Yandex | Yandex FBL signup | Yandex postmaster |
| ZOHO | ZOHO FBL signup | does not provide |
MessageBird Blog | All You Need To Know About Gmail’s Feedback Loop Offering