How do FBL reports work with forwarding and IP addresses?

Key findings

• FBL mechanism: FBL reports are predominantly sent to the IP address that delivered the email to the reporting mailbox provider, often referred to as the last hop IP.
• Forwarding challenges: When an email is forwarded, the forwarding server becomes the 'sender' in the eyes of the recipient's FBL system. If the forwarded email is marked as spam, the FBL report points back to the forwarding server's IP.
• Reputation impact: This mechanism means forwarding servers can incur reputation damage, including potential blacklisting or blocklisting, even when they are not the originators of the spam.
• Authentication methods: While Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) are crucial for email authentication, forwarding can sometimes break these validations. You can learn more about how email forwarding and DMARC policies affect delivery and reporting.
• RFC guidelines: RFC 6449, a key document on Complaint Feedback Loop Operational Requirements, emphasizes that FBL systems identify the responsible mail server by the IP address used for delivery. You can review the RFC 6449 document for more details.

Key considerations

• User education: For services that involve email forwarding, it is essential to educate users on the proper way to handle unwanted emails, specifically to avoid marking forwarded messages as spam.
• Monitoring FBLs: Regularly monitoring FBL reports, even for forwarding services, is crucial. This helps in identifying abuse patterns quickly and preventing severe blocklisting issues. Understanding how email blacklists actually work can further aid this.
• Technical mitigation: While challenging, implementing technical solutions, such as configuring recipient mailboxes to ignore certain forwarding hops for spam checking, can provide some relief.
• Reputation management: Proactive reputation management is vital for any IP engaged in email delivery, including those used for forwarding. What happens when your IP gets blocklisted highlights the consequences.

Key opinions

• Attribution confusion: Many marketers question whether FBL reports should be based on the original Return Path address or the intermediate forwarding IP, highlighting a desire for clearer attribution.
• Inadvertent involvement: Some marketers find themselves inadvertently involved in the delivery of spam when offering forwarding services, even without originating the unsolicited emails. This contributes to email deliverability issues.
• Balancing act: There's a constant struggle to balance the need to filter spam with the commitment to deliver all legitimate, expected messages to customers who rely on forwarding services.
• User behavior: Marketers frequently express the difficulty in educating end-users not to mark forwarded mail as spam, even if it appears to be spam, as this negatively impacts the forwarding server's reputation.

Key considerations

• Monitoring: It is critical for marketers running forwarding services to diligently monitor their IPs for any signs of blocklisting or reputation degradation.
• Policy adjustments: Some consider stopping forwarding services entirely if the reputational cost outweighs the benefits, especially if it leads to their IPs being added to a blocklist.
• FBL utilization: Email marketers should sign up for relevant FBLs to actively receive spam complaint reports and understand their complaint rates. More information can be found on how FBLs enhance email management.
• Authentication impact: The challenges with forwarding highlight the complexities of SPF, DKIM, and DMARC alignment and how they affect email deliverability. For example, knowing how email service providers process FBL emails can be helpful.

Key opinions

• Last hop IP: Experts confirm that FBL reports are typically based on the IP address that performed the last delivery to the reporting system, aligning with standard FBL design.
• Forwarding dilemma: The act of forwarding email, even if not originating spam, can lead to the forwarding server's IP being impacted by FBLs, creating a 'forwarding problem'.
• Operational impact: Some organizations have ceased forwarding services due to the excessive trouble and blocklisting consequences resulting from spam complaints on forwarded messages.
• Client education: A key piece of advice from experts is to strongly encourage or require customers of forwarding services never to mark forwarded emails as spam.
• Design intent: FBL systems are fundamentally designed to identify the last mail server that injected a message into a recipient's system, which explains the reliance on the last hop IP.

Key considerations

• Reputation risk: The risk of IP and domain reputation damage is significant for forwarding services, making careful management essential.
• Spam filtering: Implementing robust spam filtering on forwarding servers is crucial, even though it doesn't solve the FBL attribution problem, it helps reduce the volume of spam being forwarded.
• Community engagement: Engaging with communities like Mailop.org can provide valuable insights and solutions from other operators dealing with similar forwarding challenges.
• Policy enforcement: For specific providers, like Gmail, understanding their FBL mechanisms and best practices for implementation is key. Details can be found in discussions about Gmail's Feedback Loop operation.
• DMARC and forwarding: The interplay between email forwarding and DMARC policies can further complicate deliverability, as DMARC requires alignment of sending domains. This makes understanding how DMARC impacts email forwarding even more critical.

Key findings

• Last hop principle: Documentation often defines FBLs as mechanisms that report complaints to the entity responsible for the final delivery of the message to the recipient's mailbox, which is the last hop IP.
• RFC 6449: This RFC specifically details the operational requirements for Complaint Feedback Loops, confirming that the reporting mechanism ties complaints to the IP address from which the mail was received by the FBL participant.
• Identifying source: FBLs are designed to provide actionable data for identifying abusive sending patterns, and this is best achieved by identifying the most recent sending source. Abusix documentation describes how FBLs enhance email management.
• FBL enrollment: Mailbox providers usually require enrollment of specific IP addresses or domains to receive FBL reports, directly linking these reports to the registered sending entities. This is consistent with how ISPs use DKIM domains for Feedback Loops.

Key considerations

• Data accuracy: While FBLs report the last hop, the original sender's identity is usually embedded within the email headers, allowing for deeper investigation if necessary, though FBLs don't directly report this.
• RFC compliance: Understanding RFCs related to email, such as RFC 6449, provides a foundational knowledge for anticipating how FBLs will behave in various email routing scenarios.
• FBL purpose: The primary purpose of an FBL is to inform the responsible party of complaints, thereby empowering them to manage their sending practices and reduce spam, as highlighted by Captain Verify's blog on how the feedback loop works.
• Authentication standards: Documentation for SPF, DKIM, and DMARC outlines how these protocols work, but also implicitly reveals why forwarding can be problematic for maintaining authentication and avoiding FBL triggers on intermediate IPs.