How do ESPs handle unsubscribe feedback loops?

Feedback loops (FBLs) are mechanisms through which mailbox providers like Yahoo, Microsoft, and others report spam complaints back to senders. When a subscriber clicks "Report Spam" or "Mark as Junk" in their email client, the mailbox provider notifies the sender (or their ESP) through the FBL. ESPs that participate in these feedback loop programs receive near-real-time notification of complaints, allowing them to immediately suppress the complaining address and provide complaint data to senders for analysis and list management.

When an ESP receives a feedback loop report, they typically automatically unsubscribe the complaining address from the sender's list and add it to the suppression list. This happens without sender intervention-the ESP recognizes that continuing to send to someone who complained would damage both the sender's reputation and the ESP's shared infrastructure. The complaint is also logged and often surfaced in the sender's dashboard or analytics, allowing visibility into complaint rates and identification of problematic campaigns or list segments that generate excessive complaints.

Not all mailbox providers offer feedback loops (notably, Gmail does not provide traditional FBL access to most senders), and participation requirements vary. ESPs generally handle FBL enrollment and management as part of their service, registering their sending IPs and domains with participating providers. For senders, the key implication is that spam complaints result in automatic unsubscription through your ESP's FBL processing, even if the subscriber never clicked your unsubscribe link. This is appropriate behavior-a spam complaint is an unsubscribe expressed through the mailbox provider rather than your interface. Feedback loops turn subscriber frustration into actionable data-complaints you can learn from and addresses you immediately stop contacting.