How to implement the Gmail feedback loop ID and what are Gmail feedback loop reports?
Michael Ko
Co-founder & CEO, Suped
Published 8 Jun 2025
Updated 14 Aug 2025
6 min read
Summary
The Gmail Feedback Loop ID (FBL-ID) is a mechanism primarily designed for large-volume email senders, especially Email Service Providers (ESPs), to identify specific campaigns that generate a high volume of spam complaints from Gmail users. While the traditional feedback loop often involved direct reports, Gmail's approach has largely evolved to integrate this data into Google Postmaster Tools. Understanding how to implement the FBL-ID and interpret its reports is crucial for maintaining a healthy sender reputation and optimizing email deliverability.
Key findings
Purpose: The Gmail Feedback Loop is primarily for identifying campaigns with high spam complaint rates, especially useful for ESPs to pinpoint problematic clients.
Implementation: Implementation involves embedding a specific header (Feedback-ID) into your email campaigns.
Reporting: While some legacy users might receive direct CSV reports, most senders (and ESPs) access FBL data via Google Postmaster Tools, where complaint rates are reported as percentages.
Thresholds: Reports are typically generated only when complaint volumes exceed a certain threshold, indicating significant issues.
Key considerations
Data granularity: The FBL-ID allows Google to break down spam complaints by specific identifiers (e.g., client IDs), offering valuable insights for ESPs.
Proactive monitoring: Don't wait for FBL reports to act. Regularly monitor your complaint rates within Postmaster Tools to catch issues early.
Impact on reputation: High complaint rates, indicated by FBL data, can severely damage your sender reputation and lead to reduced inbox placement. Addressing these is crucial for improving Gmail deliverability.
What email marketers say
Email marketers often seek direct ways to implement and receive feedback loop data to improve their campaigns. There's a common desire for granular data to understand why emails are marked as spam and to respond to abuse complaints. Marketers' experiences highlight the varied nature of FBL reporting and the primary importance of general sender reputation metrics.
Key opinions
Direct implementation: Marketers are interested in adding the Feedback Loop ID (Feedback-ID) header to their email source code.
Report expectations: Many expect to receive direct reports, possibly in CSV format, detailing spam complaints.
Understanding FBL evolution: There's sometimes confusion about whether Gmail still sends direct FBL reports or if data is solely in Postmaster Tools.
Header placement: The Feedback-ID should be added to the email header for it to be recognized by Gmail.
Data actionability: While FBL-ID helps identify problematic segments, it's essential to have processes in place to act on this data, for example, by removing unengaged subscribers.
Holistic view: Don't rely solely on FBL data. Monitor other metrics in Postmaster Tools like IP and domain reputation, as well as spam rates for a comprehensive view of deliverability.
Marketer view
Email marketer from Email Geeks asked for guidance on how and where to implement the Gmail feedback loop code in the source code.
29 Jul 2019 - Email Geeks
Marketer view
Email marketer from Email Geeks confirmed that adding the code to the header is the correct approach and planned to monitor the results.
29 Jul 2019 - Email Geeks
What the experts say
Deliverability experts clarify the often-misunderstood nature of Gmail's Feedback Loop. They emphasize that while a traditional FBL concept existed, it has largely been superseded by data provided in Google Postmaster Tools. The FBL-ID is primarily a tool for ESPs to segment and attribute spam complaints to specific clients or campaigns, rather than a system for sending out direct, detailed complaint reports to all senders.
Key opinions
FBL evolution: Gmail's FBL has largely morphed into Postmaster Tools, which reports complaint percentages on its website.
ESP focus: The FBL identifier is mainly for ESPs to break down complaints per customer, aiding their internal management and remediation.
Legacy reports: Some senders might have received (or still receive) direct CSV reports if they were part of an older beta program before Postmaster Tools existed.
Spam complaint triggers: Reports (whether direct or via Postmaster Tools) are typically triggered only when complaint rates are significantly high, indicating a serious issue.
Key considerations
Granular data access: The Feedback Loop Identifier (FBL-ID) allows Google to attribute spam complaints to specific campaign IDs or customer segments, providing valuable insights for ESPs and large senders.
Interpreting silence: If you don't receive direct FBL reports, it often means your complaint rates are below Google's threshold, which is generally a good sign.
Expert view
Deliverability expert from Email Geeks explains that the Gmail Feedback Loop is primarily useful for ESPs to identify their different clients using a 'client ID' or 'gmail FBL ID' header.
29 Jul 2019 - Email Geeks
Expert view
Deliverability expert from Email Geeks clarified that Gmail typically doesn't send direct FBL reports to most senders anymore, stating that Postmaster Tools is where percentages are reported.
29 Jul 2019 - Email Geeks
What the documentation says
Official documentation outlines the precise method for implementing the Gmail Feedback-ID and details the types of reports available to senders. It stresses that the FBL is primarily for large-volume senders, enabling them to gain insights into specific campaign performance regarding spam complaints. This information is predominantly accessed through Google Postmaster Tools, rather than via direct email reports for most users.
Key findings
Target audience: The Gmail Feedback Loop is designed for large volume senders, not individual users.
Data availability: Feedback loop data is primarily available within Google Postmaster Tools, showing complaint rates for specific campaigns or identifiers.
Actionable insights: The FBL aims to help senders identify which specific campaigns are generating high spam reports, allowing them to take corrective action.
Key considerations
Header uniqueness: The Feedback-ID should be unique enough to allow granular tracking (e.g., per customer, per campaign) without revealing sensitive user data.
Postmaster Tools integration: Senders must register their domains in Google Postmaster Tools to access FBL data and other crucial deliverability metrics, like spam rate dashboards and IP reputation, which can be viewed in the spam rate dashboard.
Data limitations: Gmail's FBL data does not provide individual recipient email addresses, only aggregated complaint rates associated with the Feedback-ID.
Technical article
Google's documentation confirms that the Feedback Loop (FBL) allows large volume senders to identify campaigns with a high volume of complaints from Gmail users. This tool is particularly useful for pinpointing problematic email streams.
29 Jul 2019 - Google Help
Technical article
AWS documentation explains that Google Postmaster Tools guides you through implementing and using Feedback Loops to identify email campaigns receiving high complaint volumes, which is crucial for Amazon SES email senders.
