|Yahoo Mail Spam Button|
The process works like this:
- Let's say you're an AOL or Outlook.com or Yahoo user.
- You've received a message that you didn't want to receive (assumably because it is spam).
- You click on the "this is spam" or "report spam" button in the user interface of your email provider.
- A complaint is silently and automatically sent back to the sender or to the sender's ISP (Internet Service Provider) or ESP (Email Service Provider).
- The person who complained (you) will be unsubscribed and should not receive any further mail from that sender.
- That spam complaint is logged by your webmail provider or the sender's email service provider.
- Senders who have too many complaints probably will get blocked by your webmail provider.
The main feedback loops M3AAWG lists are: AOL, Bluetie/Excite, Comcast, Cox, Earthlink, Fastmail, OpenSRS, Microsoft Outlook.com JRMP, QQ.com, Rackspace, RoadRunner/Time Warner Cable, Synacor, Telenor, Terra, USA.net, United Online/Juno/Netzero, Zoho, XS4ALL and Yandex.
These are the "traditional, IP address-based" feedback loops. Your ESP typically has signed up for all of these feedback loops for you. If you're not using an ESP and you need to sign up yourself, the M3AAWG page has links to information and how to sign up for each.
M3AAWG lists two additional domain-based feedback loops: Yahoo and Mail.ru.
Your ESP probably does NOT sign you up for these feedback loops automatically. Because they are domain-based feedback loops, the ISP (Yahoo and Mail.ru) requires that mail be authenticated with DKIM authentication. Usually your domain has to be registered directly with the ISP. DKIM is usually not enabled by default by an email service provider; contact your ESP or mail platform vendor for more information as needed.
M3AAWG also lists some additional non-standard things that they call Feedback Loops. They call these "aggregated FBLs." These include Gmail, Outlook.com SNDS, Mail.ru and Signal Spam.
These are not feedback loops. In other words, they do not provide information back that allows you to unsubscribe people who complain -- the core function of a "traditional" feedback loop. They still provide value in that they provide you the sender, or your ESP or ISP, aggregated data regarding your deliverability statistics and sending reputation. Indeed, M3AAWG clarifies that "this format does not provide the sender with the full message and does not identify the user who complained about the email."
People ask me about this "Gmail FBL" in particular so let me explicitly clarify: What this is saying is, no, the Gmail "feedback loop" does not allow you to unsubscribe people who complain about your mail.
Microsoft Outlook.com's SNDS (Sender Network Data Services) portal is a useful interface where you register to be able to look up reputation data specific to your sending IP addresses. Very helpful, though like the Gmail functionality, it does not itself allow you to unsubscribe complainers. Microsoft has separate functionality called JMRP (Junk Mail Reporting Program) that provides the ability to unsubscribe people who complain.
Of course, keep in mind that feedback loop participation does not mean you can get away with not having opt-in permission before sending mail. These ISPs provide this data back to senders as a courtesy, but they actually primarily use this data to calculate complaint rates and decide which senders might merit blocking. Lack of permission gets you high complaint rates. High complaint rates will get you blocked. Giving somebody you've spammed the opportunity to unsubscribe will not stop you from getting blocked. Permission still matters very much in 2016.
(Note: If you didn't already know, M3AAWG is pronounced "MAAWG" (without the 3) and rhymes with frog.)