An email feedback loop (aka ISP feedback loop or complaint feedback loop) is a spam reporting mechanism implement by an internet service provider (ISP) or mailbox provider (MBP) that allows spam complaints to flow back to the sender or sender's email platform. Those forwarded "report spam" notifications allow the sender or sending platform to unsubscribe those who complain and also to provide sender feedback to understand which clients, lists or campaigns are causing the highest number or percentage of spam complaints.

ISPs and MBPs already collect and correlate spam complaint data for their own uses. When you click the "report spam" button in Gmail, or, Yahoo, or elsewhere, those services capture and log your complaint, to feed into their internal spam filtering systems, to generate reputation-related metrics about the sender. Senders who generate more spam complaints are more likely to find themselves blocked, or to find their mail relegated to the spam folder. High spam complaints are not the only reason you can end up with a deliverability issue, but it often can be the underlying cause.

It is specifically the "feedback loop" component of this process that allows complaints to also be forwarded back to the sender or the sender's email platform. Feedback loops are valuable because they provide reputation-related data points back to the email sender. If you get blocked by an ISP and you're wondering why, being able to figure out if a particular list or segment was garnering high complaints before the blocking started is often a strong indicator of what may have caused the blocking issue.

A variety of ISPs and MBPs offer FBLs:

  • A company called Validity manages FBLs for a large number of ISPs. These are all managed via a single "Universal Feedback Loop" interface. Their Universal Feedback Loop service covers these internet service providers and mailbox providers: BlueTie, Comcast, Cox, Fastmail, Gandi, ItaliaOnline, LiberoMail, Virgilio,, Liberty Global, UnityMedia, UPC, Locaweb,, OpenSRS, Rackspace,, SFR, SilverSky, Swisscom, Synacor, TIM, Telenet, Telenor, Telstra, Terra, UOL, Virgin Media, XS4ALL, Yandex, and Ziggo.

Besides those, there are two other large ISP FBLs that are very important.

  • Yahoo: Yahoo's FBL is called the CFL and you can find more information here. Yahoo's feedback loop is unique compared to most others, in that you register your sending domain, and the FBL only covers (will only send reports about) mail that is properly authenticated with DKIM authentication. (All your mail should be authenticated with DKIM nowadays, anyway.)
  • Microsoft: Microsoft's FBL is called the JMRP (Junk Mail Reporting Program) and you can find more information here. For those familiar with Microsoft's Sender Network Data Services (DNS) portal, you'll note that the SNDS portal is where you go to configure this FBL -- sign up for SNDS access first, then you can create a JMRP feed and include all of your SNDS-approved IP addresses in that JMRP feed.

Here are three other things that are either not FBLs or are otherwise not available:

  • AOL: AOL is no longer a separate mailbox provider -- it is effectively now a part of Yahoo. If you are signed up for the Yahoo CFL, you're also signed up to receiving FBL reports for AOL users. There is no longer a separate AOL feedback loop.
  • Earthlink: American broadband provider Earthlink offered a feedback loop at one time, and it's possible that FBLs set up with them many years ago may still even be working. However, Earthlink has been non-responsive to requests to update or add FBLs for a long time now, so don't plan on signing up for an Earthlink FBL any time soon. Any guidance that suggests that you should go sign up for this FBL is probably based on years-old information.
  • Gmail: Google confusingly uses the term Feedback Loop to refer to a certain type of reputation feedback that is provided about sends to Gmail. The data is useful; but it's not a feedback loop as defined here. You don't receive complaint data back in a way that would allow you to unsubscribe specific people who complain. You can find more information here.

ESPs, CRMs and marketing automation platforms often sign up all clients for all or most FBLs automatically. If you're a client of a CRM or ESP platform, you should ask their support whether or not they do this automatically. Typically, registering for an FBL requires proving that you own or manage a given sending IP address (or domain, in the case of Yahoo). Unless you own the sending platform, you may not own the IP addresses and may not be able to register for FBLs.

Want to learn more about deliverability terminology? If so, be sure to visit the DELIVTERMS section here on Spam Resource.

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