When someone marks your email as spam, what happens? If you're not enrolled in Feedback Loops (FBLs), the answer is: nothing. The complaint disappears into the void — and your reputation silently degrades.
This Week’s Lesson
A Feedback Loop (FBL) is a service offered by major inbox providers that forwards spam complaints back to the sender. When a Gmail, Yahoo, or Outlook user clicks 'Mark as Spam,' the ISP can notify you so you can remove that person from your list.
Yahoo and AOL both offer open FBLs that any sender can apply for. Google's FBL is through Google Postmaster Tools (covered next week). Microsoft provides complaint data through the Junk Mail Reporting Program (JMRP).
To apply for FBLs, you typically need a dedicated sending IP and DKIM signing. You register your IP, provide a complaint destination email address, and the ISP begins forwarding complaints to you.
The complaint rate threshold you need to stay below is roughly 0.08-0.1% for Google and 0.3% for Yahoo. Exceeding these thresholds can trigger bulk filtering where all your email goes to spam, or even outright blocking.
FBL data is gold. Each complaint tells you: this person doesn't want your email. Whether that means removing them from all lists, re-evaluating your onboarding, or auditing your content depends on the patterns you find.
Without FBL data, you're flying blind on the most important deliverability signal there is: whether recipients actually want what you're sending.