How do I know if my IP is on a blacklist due to forwarding?

You can check if your IP is on a blacklist by using various online blocklist checking tools. Many Mailbox Providers also offer postmaster tools, like Gmail's Postmaster Tools , that provide insights into your IP reputation and spam rates. Consistently high complaint rates on your FBL reports are a strong indicator of potential blocklisting.

Can DMARC help with FBL issues caused by forwarding?

DMARC helps with email authentication and policy enforcement, which can improve overall deliverability and reduce spoofing. However, it doesn't directly solve FBL issues caused by forwarding because FBLs are typically tied to the last hop IP address, not DMARC alignment. While a strong DMARC policy helps your domain's reputation, the forwarding server's IP is still at risk if it delivers spam.

What is an aggregate FBL and how is it different?

An Aggregate FBL (like those discussed by M3AAWG ) is an alternative to traditional IP-based FBLs. Instead of individual complaint messages, it provides aggregated counts of complaints by IP, domain, or other identifiers over a period. This format offers a summarized view, which can be easier to process for high-volume senders, but it still relates complaints to the sending entity, whether an IP or a domain.

Are all FBLs IP-based?

No, not all FBLs are strictly IP-based. While most major Mailbox Providers rely on the last hop IP address for FBL reports, some, like Yahoo, also offer domain-based FBLs that link complaints to the DKIM signing domain. It's essential to check the specific requirements for each Mailbox Provider's FBL program.

How can I minimize FBL complaints for forwarded mail?

Minimizing FBL complaints for forwarded mail involves a multi-pronged approach. Ensure you're not forwarding emails that are clearly spam. Educate your users on not reporting forwarded mail as spam to the forwarding service. If possible, encourage them to unsubscribe from unwanted senders or report spam to the original sender. Finally, maintain excellent sender reputation on your forwarding IPs to reduce the likelihood of issues.

How do FBL reports work with forwarding and IP addresses? - Sender reputation - Email deliverability - Knowledge base

Understanding how Feedback Loop (FBL) reports work is critical for maintaining a healthy sender reputation and ensuring your emails reach the inbox. FBLs are essentially complaint notifications sent by Mailbox Providers (ISPs) when their users mark your emails as spam. Receiving these reports allows you to identify problematic campaigns or segments of your mailing list and take corrective action, like suppressing subscribers who complain.

However, the dynamics become more complex when email forwarding is involved. If you or your users employ mail servers that forward emails to a final destination, the way FBL reports are generated and who receives them can become a tricky issue. It can significantly impact your sending IP's reputation, even if you weren't the original sender of the problematic email.

This challenge often leads to confusion, especially concerning whether FBL reports are tied to the Return-Path address or the last hop IP address. I will explain how these mechanisms interact and what you need to know to navigate the complexities of FBL reporting in scenarios involving email forwarding.

Understanding feedback loops

Feedback loops, or FBLs, are a fundamental part of the email ecosystem designed to combat spam and protect user experience. When a recipient clicks the report spam button, the Mailbox Provider (such as

Gmail or

Yahoo) generates a complaint report. This report is then sent back to the IP address or domain registered to receive these specific FBLs.

The primary purpose of FBLs is to provide direct insight into subscriber engagement and satisfaction. By informing senders about complaints, Mailbox Providers empower them to clean their mailing lists, improve content, and avoid practices that lead to negative user feedback. Failing to act on these reports can lead to significant deliverability issues, including emails landing in the spam folder or even being blocked entirely.

While most FBLs are IP-based, some, like Yahoo's FBL, can also be domain-based, using DKIM signing practices. Regardless of the specific mechanism, the goal is consistent: to alert senders about user complaints so they can maintain a positive sender reputation and avoid common pitfalls that lead to email blacklists (or blocklists). Understanding how email blacklists actually work is crucial for any sender.

The role of IP addresses in FBL reporting

For most FBL systems, the critical piece of information used to identify the sender for a complaint report is the IP address from which the email was delivered to the Mailbox Provider's servers. This is known as the last hop IP. When a Mailbox Provider receives an email, it logs the IP address of the sending server. If that email is subsequently marked as spam by a user, the FBL report is generated and sent to the entity that owns or manages that specific IP address.

This mechanism ensures that the feedback goes directly to the server responsible for delivering the problematic email to the ISP's network. It's a pragmatic approach because the ISP's system only sees the immediate connection. It doesn't necessarily trace back to the original sender's IP if the email passed through multiple intermediate servers or forwarders.

The Return-Path address, while important for bounce management, typically plays a secondary role in FBL processing compared to the last hop IP. While some FBLs may use elements from the email headers, the definitive factor for most IP-based FBLs is the IP that made the direct connection. This is why managing your sending IPs and their associated FBL registrations is paramount.

IP-based FBLs

Many major Mailbox Providers, including Google and

Microsoft, primarily rely on the sending IP address for FBL reports. This means if you're sending email, the IP address used to connect to their servers must be registered for their respective FBL programs.

Best practice

Always register the IPs you use for sending with the relevant Mailbox Provider FBL programs. This ensures you receive timely complaint data to protect your sender reputation. If you’re not receiving FBL reports, it might be due to un등록ed IPs.

Email forwarding and its FBL implications

Email forwarding is a common practice where an email sent to one address is automatically redirected to another. While convenient for recipients, it introduces complexities for FBL reporting. When an email is forwarded, the forwarding server essentially takes on the role of a new sender from the perspective of the final Mailbox Provider. If the recipient of the forwarded email marks it as spam, the FBL report will be generated against the forwarding server's IP address, not the original sender's.

This can lead to significant problems for operators of forwarding mail servers. Even if they are not originating spam, they become involved in its unfortunate delivery. The forwarding server's IP can accumulate spam complaints, leading to a damaged reputation, increased bounce rates, and even blacklisting (or blocklisting) on various email blocklists. This can happen even if the original sender is legitimate but the content is perceived as spam by the end recipient.

Consider a scenario where a user, Adam, has a self-hosted mail server that forwards incoming email to his

Fastmail address. If an email is sent to Adam's server, forwarded to Fastmail, and then Adam marks it as spam at Fastmail, the FBL report will go back to Adam's forwarding server's IP. This is because Adam's server was the last hop that delivered the email to Fastmail's system. This clearly highlights the challenge of IP-based FBLs with forwarding.

Direct sending

FBL attribution: FBLs are directly tied to your originating sending IP or domain.
Reputation management: You receive FBLs for emails you directly sent, allowing precise list hygiene.
Control: Full control over sender reputation based on your own sending practices.

Forwarding

FBL attribution: FBLs are tied to the forwarding server's IP, even if it's not the original sender.
Reputation management: Forwarding server's IP can suffer reputation damage from others' spam.
Control: Limited control over the content and spam complaints of forwarded emails.

Strategies for managing FBLs with forwarding

Given that FBL reports primarily target the last hop IP, managing email forwarding effectively requires specific strategies to protect your sender reputation. One technique sometimes employed is the Sender Rewriting Scheme (SRS), which rewrites the Return-Path address during forwarding to ensure bounces return to the original sender. However, SRS doesn't alter the last hop IP, so it doesn't prevent FBL complaints from hitting the forwarding server.

A key strategy for any email sender, including those operating forwarding services, is diligent monitoring of blocklists (or blacklists). If your IP is frequently listed, it can severely impact deliverability. Regularly checking your IP status is essential. You can monitor your IPs against major email blocklists to detect and address any listings promptly.

For forwarded mail, it is challenging to control recipient behavior. However, educating your users or customers about the implications of marking forwarded mail as spam could be a helpful, albeit difficult, step. The ideal scenario is for recipients to unsubscribe or directly report spam to the original sender, rather than hitting the spam button on a forwarded email. This is often where Mailbox Providers seek a Complaint Feedback Loop Address Header for clarity.

Additionally, ensuring proper email authentication is crucial, even with forwarding. While DMARC policies can affect email delivery and reporting by indicating how Mailbox Providers should handle unauthenticated emails, it won't prevent FBLs generated against the forwarding IP. However, having SPF, DKIM, and DMARC configured correctly is a baseline requirement for any legitimate sender, especially since email forwarding itself can impact SPF, DKIM, and DMARC validation.

Views from the trenches

Best practices

Actively monitor your IP addresses for any blocklist listings, as forwarding can inadvertently lead to issues.

If you operate a forwarding service, ensure your IPs are registered for all relevant Mailbox Provider FBL programs.

Implement DMARC for your domains to improve overall email authentication and reporting, even if it doesn't directly solve FBL forwarding issues.

Consider filtering or quarantining suspected spam before forwarding to protect your IP reputation.

Common pitfalls

Assuming FBL reports will go to the original sender's IP, rather than the forwarding server's IP.

Not monitoring the reputation of your forwarding IPs, leading to unexpected blocklistings.

Underestimating the impact of forwarded spam on your infrastructure's deliverability.

Relying solely on SRS to solve all deliverability issues related to forwarded mail.

Expert tips

For large-scale forwarding, consider dedicated IP ranges and rigorous abuse desk monitoring.

Develop clear policies for handling spam complaints on forwarded mail, even if difficult to enforce.

Leverage aggregate FBL formats where available, as they can provide more comprehensive data.

Engage with Mailbox Providers' postmaster teams for specific guidance on forwarding challenges.

Expert view

Expert from Email Geeks says that typically spam reports based on IPs have always gone to the address that delivered the email to the reporting system, which is what should be expected from any FBL system.

January 17, 2023 - Email Geeks

Expert view

Expert from Email Geeks says that some forwarding services stopped forwarding mail because customers ended up reporting spam that hit their IPs, causing too much trouble.

January 17, 2023 - Email Geeks

Key takeaways for FBLs and forwarding

Feedback Loop reports are indispensable for managing sender reputation, providing direct signals from Mailbox Providers about user complaints. While their mechanism is straightforward for direct sending, the inclusion of email forwarding adds a layer of complexity. Crucially, most FBL reports are attributed to the last hop IP address that delivered the email to the Mailbox Provider, not necessarily the original sender or the Return-Path.

This means that mail servers involved in forwarding, whether self-hosted or part of a service, can inadvertently accumulate spam complaints and suffer reputation damage, including being placed on email blocklists (or blacklists), even if they did not originate the spam. It is a constant balancing act between ensuring deliverability for legitimate emails and preventing abuse.

Proactive management involves diligently registering IPs with FBL programs, consistent blocklist monitoring, and careful consideration of how forwarding impacts your IP reputation. By understanding these dynamics, you can better protect your email infrastructure and ensure your legitimate messages continue to reach their intended recipients.