Feedback Loop(FBL)
A service provided by ISPs that reports spam complaints back to senders.
Definition
A Feedback Loop (FBL) is a mechanism where Internet Service Providers (ISPs) report spam complaints from their users back to the original email sender. When a recipient marks your email as spam, the ISP sends a notification to your registered FBL address, allowing you to remove that person from your list and investigate the cause.
Why It Matters
FBL data helps you maintain list quality and protect your sender reputation. High complaint rates damage deliverability. By receiving immediate feedback about complaints, you can remove complainers, identify problematic campaigns, and adjust your practices before your reputation suffers.
How It Works
You register for FBL programs with major ISPs (like Yahoo, Microsoft, Comcast). When their users mark your email as spam, the ISP sends a report to your registered address containing the original email and the complainer's address. Your ESP should process these automatically and suppress complainers.
Best Practices
- 1Register for FBL programs with all major ISPs
- 2Remove complainers from your list immediately
- 3Monitor complaint rates by campaign to identify issues
- 4Aim for complaint rates below 0.1%
Feedback Loop Provider Table
| Provider | Feedback type | Notes |
|---|---|---|
| Yahoo/AOL | Traditional spam complaint reports | Usually handled through ESP infrastructure |
| Microsoft | Complaint and reputation signals | Includes Outlook and Hotmail ecosystems |
| Comcast and other ISPs | Traditional FBL reports | Coverage varies by provider |
| Gmail | Postmaster Tools, not traditional recipient-level FBL | Shows aggregate reputation and complaint signals |
Feedback Loop Response Table
| Complaint signal | Immediate action | Follow-up |
|---|---|---|
| Single subscriber complaint | Suppress that address | Confirm automation is processing FBL reports |
| Campaign complaint spike | Pause similar sends | Review audience source, subject, and offer |
| Provider-specific complaints | Reduce volume to that provider | Check provider reputation dashboard |
| Repeated source complaints | Stop that acquisition source | Audit consent and expectation setting |
FBL Metric Table
| Metric | Healthy target | Why |
|---|---|---|
| Complaint rate | Below 0.1% | Higher rates threaten inbox placement |
| Time to suppress | Immediate or near-immediate | Prevents sending again to people who complained |
| Complaints by campaign | Lower than baseline | Finds problematic messages |
| Complaints by source | Stable across acquisition channels | Reveals bad lead sources or unclear consent |