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Summary

Decoding Comcast Feedback Loop (FBL) email addresses for unsubscription purposes presents a unique challenge for email senders. Unlike some other FBLs, Comcast often masks the actual recipient's email address with a one-way hash, meaning the original address cannot be directly retrieved from the FBL report itself. This design is primarily for privacy, preventing third parties from identifying complainers without proper authorization to access the sender's internal systems. While the direct email address isn't available, senders must rely on other identifying information within the FBL data or their own internal tracking to correctly identify and unsubscribe the complaining user from their lists. Understanding how different inbox providers, including Comcast, handle feedback loops is crucial for effective list management and maintaining a positive sender reputation.

What email marketers say

Email marketers often grapple with the intricacies of Feedback Loops (FBLs), particularly when dealing with providers like Comcast that mask user identities. While the goal is always to promptly unsubscribe users who complain, the technical limitations of FBL data can complicate this process. Marketers emphasize the importance of robust internal systems that can cross-reference FBL data with their subscriber lists, even without a direct email address. This often involves embedding unique identifiers in email headers to facilitate matches.

Marketer view

Email marketer from Email Geeks explains that they were exploring the Comcast FBL service and noted the masked email addresses. They were initially confused about how to decode these to unsubscribe users, especially without manually sifting through MTA logs for timestamps. This highlights a common initial hurdle for senders new to Comcast's FBL.

10 Mar 2021 - Email Geeks

Marketer view

Marketer from Email Geeks mentioned they observed that Comcast's system seemed to be calling the unsubscribe URL from their email's List-Unsubscribe header. This led to an assumption that the subscriber was automatically unsubscribed, which can be misleading if the internal list management logic isn't aligned. It implies a need for a deeper understanding of the interplay between FBLs and List-Unsubscribe functionality.

10 Mar 2021 - Email Geeks

What the experts say

Email deliverability experts agree that the hashing of email addresses in Comcast FBL reports is a deliberate privacy measure. They emphasize that direct decoding of these hashes is not possible, as they are designed to be one-way. The key for senders lies in their own internal systems, specifically in embedding unique identifiers within the email headers. This allows the sender to match the FBL complaint data with their own subscriber records, ensuring compliance and proper list hygiene without compromising user privacy. Experts also caution against assuming certain FBL behaviors, such as direct List-Unsubscribe header triggers, unless explicitly confirmed by the ISP.

Expert view

Expert from Email Geeks clarified that the masked Comcast FBL email address is a one-way hash and therefore cannot be decoded. This fundamental technical reality means that senders cannot directly reverse-engineer the original email from the FBL report itself.

10 Mar 2021 - Email Geeks

Expert view

Expert from Email Geeks elaborated that the one-way hash protects third parties from identifying the complainer. However, it's not meant to prevent the original sender from identifying them and taking necessary actions, provided they access their own systems with appropriate permissions and legal constraints. This explains the privacy rationale behind Comcast's approach.

10 Mar 2021 - Email Geeks

What the documentation says

Technical documentation and RFCs often outline the principles behind Feedback Loops and privacy considerations. While specific ISP documentation for Comcast FBLs is typically private or only accessible via direct relationships, general FBL RFCs (like RFC 5965, defining Abuse Reporting Format) specify the structure and purpose of FBL reports. These documents clarify that FBLs are mechanisms for ISPs to relay user complaints to senders, enabling them to take appropriate action, such as removing complainers from their lists. The masking of recipient addresses is a common privacy feature, ensuring that sensitive user data is not widely exposed while still providing actionable intelligence to the sender.

Technical article

Documentation from RFC 5965, which defines the Abuse Reporting Format for FBLs, states that reports should include sufficient information to allow the message originator to identify the specific message and, where possible, the specific recipient who generated the report. However, it also emphasizes that privacy concerns may necessitate anonymization of recipient addresses.

25 Aug 2010 - RFC 5965

Technical article

Postmaster documentation from a major ISP's guide on FBLs indicates that recipient addresses in complaint feedback reports are often transformed into an opaque identifier (a hash or token) to protect user privacy. Senders are expected to use this identifier, along with other email headers, to correlate the complaint with their internal subscriber database.

12 Apr 2022 - Major ISP Postmaster Guide

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