Back to Glossary
Deliverability

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%

Frequently Asked Questions

Major FBL providers include Yahoo/AOL, Microsoft (Outlook, Hotmail), and Comcast. Gmail does not offer a traditional FBL but provides data through Postmaster Tools. Most ESPs handle FBL registration for you.

Keep complaint rates below 0.1% (1 complaint per 1,000 emails). Above 0.1% starts to impact deliverability. Above 0.3% is problematic and may trigger spam filtering or account issues.