FBL (Feedback Loop)
Learn what a Feedback Loop (FBL) is, how it reports spam complaints, and how DMARCeye uses FBL data to protect sender reputation and deliverability.
What is a FBL (Feedback Loop) in email?
A Feedback Loop (FBL) is a system provided by mailbox providers that reports when recipients mark emails as spam or junk. FBLs allow senders to receive notifications about user complaints so they can identify problematic campaigns, misconfigured mail flows, or compromised accounts. These reports are essential for maintaining sender reputation and ensuring that only wanted messages reach inboxes.
In email authentication and deliverability management, FBLs act as an early warning mechanism. They help domain owners detect when recipients perceive their messages as unwanted or suspicious, even if authentication passes through SPF, DKIM, and DMARC successfully.
How Feedback Loops Work
When a user clicks “Report Spam,” the mailbox provider sends an Abuse Reporting Format (ARF) message to the sender’s registered complaint address. These messages contain information about the recipient’s complaint, including headers and metadata that identify the source of the email.
Example FBL workflow:
- A user flags an email as spam.
- The mailbox provider generates an ARF report.
- The report is sent to the abuse or postmaster address defined in the sender’s DNS or registration with the provider.
- The sender’s system receives the report, processes it, and removes the recipient from future mailings.
Benefits of FBL Participation
- Reduces complaint rates by allowing quick suppression of unhappy subscribers
- Protects domain reputation and IP deliverability
- Detects compromised systems or spam abuse early
- Improves compliance with email marketing best practices
Mailbox providers such as Yahoo, Microsoft, and Comcast offer FBL programs. Participation often requires senders to maintain valid DNS records, publish SPF and DKIM signatures, and have a working postmaster address.
FBL and DMARCeye
DMARCeye integrates FBL data alongside DMARC aggregate reports to help organizations identify complaint trends and reputational risks. By analyzing complaint sources and matching them to IPs or domains, DMARCeye enables faster mitigation of spam incidents and policy violations.
This visibility allows domain owners to maintain a strong reputation, improve engagement, and ensure that legitimate email remains trusted and delivered effectively.
Sign up for a free trial of DMARCeye today and secure your email domain.
To learn more about DMARC and DMARC-related terms, explore the DMARCeye Glossary.