Summary
Email forwarding is a common practice, but it frequently leads to DMARC (Domain-based Message Authentication, Reporting, and Conformance) failures. This occurs because the act of forwarding often alters email headers or content, which breaks the cryptographic signatures of SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail), causing the forwarded message to fail DMARC authentication. When a mailbox provider forwards emails from several addresses on their domain to a single Gmail account, and these forwarded emails consistently fail DMARC, it raises questions beyond typical authentication issues. The core of the problem often lies in understanding the specific forwarding mechanism used by the mailbox provider and why such a consolidated forwarding setup exists.
Key findings
- DMARC challenge: DMARC is inherently designed to break when emails are forwarded, as the intermediate servers can modify headers or content, thus invalidating SPF and DKIM signatures. For more context on why these failures occur, see our guide on DMARC verification failures.
- Unusual forwarding patterns: A key observation in such scenarios is that multiple, seemingly unrelated email addresses from a single mailbox provider domain are all being forwarded to the exact same Gmail address. The Gmail username often contains a reference to the forwarding mailbox provider, suggesting an intentional (though unusual) setup.
- Beyond DMARC: While DMARC failures are the visible symptom, the underlying mystery is typically not about DMARC authentication itself, but why the mailbox provider is configured to forward emails in this specific manner.
- Suspected privacy issues: If the mailbox provider is a large, reputable service, such a widespread and consolidated forwarding pattern could indicate a fundamental privacy violation or compromised mailboxes, especially if the original addresses belong to distinct subscribers. This is a crucial area for further investigation.
Key considerations
- Verify DMARC reports: Always review your DMARC aggregate and forensic reports (if enabled) to confirm the source IP addresses of the forwarded emails. This can help identify if the forwarding is indeed coming from the suspected mailbox provider. Our article on understanding and troubleshooting DMARC reports provides more detail.
- Contact the mailbox provider: The most direct approach to resolve the mystery is to contact the postmaster or abuse desk of the mailbox provider in question. They may be able to explain their forwarding policies or investigate unusual activity. Refer to Google's official guidance on controlling unauthenticated mail from your domain.
- Assess the legitimacy: Consider if there's any legitimate reason for multiple distinct user accounts to forward to a single external Gmail address. This could range from a small business owner consolidating emails to a more concerning scenario like data harvesting or compromised accounts.
- Impact on sender reputation: Consistent DMARC failures, even if due to forwarding outside your control, can negatively impact your sender reputation. While the problem originates with the forwarder, monitoring these failures is essential for maintaining strong deliverability.
What email marketers say
Email marketers often encounter DMARC failures when their emails are forwarded, especially to services like Gmail. Their primary concern usually stems from unexpected bounce messages indicating DMARC rejection, even when their direct sending practices are sound. They describe observing patterns where multiple email addresses from the same mailbox provider appear to be forwarded to a single Gmail account, raising questions about the recipient's configuration or the mailbox provider's practices, rather than their own email authentication setup. This leads to investigations into the anomaly of the forwarding rather than a typical DMARC troubleshooting process.
Key opinions
- DMARC failure symptom: Marketers report DMARC policy failures primarily as a symptom that reveals an underlying forwarding issue, rather than a problem with their initial email authentication. They observe async bounces from Gmail, indicating DMARC rejection due to their p=reject policy.
- Peculiar forwarding pattern: It's noted that various email addresses, all from the same mailbox provider (e.g., UOL in Brazil), are being forwarded to one specific Gmail address. The username of this Gmail account often contains a reference to the mailbox provider, such as redirectionforESP@gmail.com.
- Inconsistent behavior: Despite thousands of other users at the same mailbox provider receiving emails without DMARC failures, a small, rotating set of 5-6 addresses daily exhibit this forwarding behavior and subsequent DMARC rejection. This suggests an isolated, rather than systemic, issue.
- Suspicion of compromise: Given the diverse registration data and behavior of the affected accounts, marketers find it unlikely that these are all owned by a single individual. This raises concerns about potential mailbox compromise or unauthorized forwarding activities by the mailbox provider. For more on preventing email deliverability issues, consider why Gmail might block emails.
Key considerations
- Investigate the unknown: Marketers often lack visibility into how a recipient's mailbox provider handles forwarding internally. This lack of information is the root of their confusion and requires external investigation.
- Check DMARC reports for IPs: Despite the initial confusion, reviewing DMARC aggregate reports for the source IP addresses of the failing emails is essential. If the IPs belong to the mailbox provider, it confirms their involvement in the forwarding chain. This can assist in troubleshooting. See our article on how to troubleshoot DMARC failures.
- Engage mailbox postmasters: Directly contacting the mailbox provider's postmaster team is deemed the best course of action when faced with such anomalous forwarding behavior, especially if direct inquiries yield no immediate answers.
Marketer from Email Geeks asks about experiencing DMARC policy failures due to forwarding. They note that all failures involve emails from the same ESP, forwarded to the same Gmail address, which includes a reference to the ESP in the username. They question why the ESP would implement such a forwarding setup.
Marketer from Email Geeks states that they have a reject DMARC policy and receive asynchronous bounces from Gmail about DMARC failures. They explain that all original addresses are on their list and belong to the same ESP, seemingly all forwarded to a single Gmail address. They suspect the ESP is behind this, noting that they've reached out to the postmaster without a response.
What the experts say
Email deliverability experts concur that DMARC is inherently designed to break when emails are forwarded, primarily because forwarding processes often interfere with SPF and DKIM. While SPF is almost always invalidated by forwarding, DKIM can sometimes survive if the message content and critical headers remain unaltered. The scenario of multiple accounts from a single mailbox provider forwarding to one Gmail address is considered highly unusual, prompting experts to investigate whether it's a legitimate user-configured setup, a privacy breach, or an obscure provider-side operation. They stress the importance of DMARC reports in diagnosing the source of the forwarding.
Key opinions
- DMARC and forwarding incompatibility: Experts widely agree that DMARC, by design, often breaks when emails are forwarded. This is because forwarding can alter the email's authentication path or content. For more on this, check our article on why DMARC fails even if SPF and DKIM pass.
- SPF vs. DKIM survival: In many forwarding scenarios, SPF is likely to break because the IP address of the forwarding server won't be authorized by the original sender's SPF record. DKIM, however, can sometimes survive if the forwarding process doesn't modify the signed parts of the email (e.g., subject line, body).
- Investigate the forwarding origin: The core question should shift from 'Why DMARC fails?' to 'Why are these emails being forwarded in this specific, centralized way?' Experts suggest the forwarding is usually configured by the address owner, or it could indicate a peculiar setup at the mailbox provider.
- Potential privacy concerns: If a large number of disparate accounts from a reputable mailbox provider are forwarding to a single external Gmail address, this raises serious concerns about a fundamental privacy violation or compromised mailboxes. It's an unlikely, but possible, scenario.
- Role of DMARC reports: DMARC aggregate reports are crucial for identifying the source IP addresses of forwarded emails that fail authentication. These IPs can help determine if the forwarding is indeed originating from the stated mailbox provider. You can find more information about the basics in our simple guide to DMARC, SPF, and DKIM.
Key considerations
- Distinguish between DMARC report and SMTP bounce: It's important to differentiate between an actual DMARC aggregate report (XML data) and an SMTP bounce message. While both inform of DMARC failure, the former provides structured data for analysis.
- Internal forwarding complexities: Even internal forwarding processes within a large service (e.g., G-Suite to Gmail, or via integration services like Zapier) can sometimes preserve the return path but break SPF and DKIM, leading to DMARC policy violations and subsequent bounces.
- Direct communication with the mailbox provider: The most effective step is to seek clarification directly from the mailbox provider (like UOL). They are best positioned to explain their domain configuration and any unusual forwarding setups, or to investigate potential security incidents. Consider how contacting postmasters can aid deliverability.
Expert from Email Geeks explains that DMARC is designed to break when emails are forwarded. They ask for the exact scenario and examples of addresses to better understand the issue, emphasizing that this behavior is often an intended consequence of DMARC's authentication process.
Expert from Email Geeks observes that the impact depends heavily on the specific forwarder. In many cases, forwarding will break SPF authentication, but DKIM might remain intact, which means DMARC could still pass if DKIM alignment is maintained, suggesting a nuanced understanding of forwarding impacts.
What the documentation says
Official documentation and research on email authentication protocols consistently highlight the challenges DMARC faces when emails undergo forwarding. The core principle of DMARC relies on the successful authentication and alignment of SPF and DKIM. However, when an email is forwarded, the forwarding server often acts as a new sender, which typically breaks SPF. Furthermore, if the forwarding server modifies any part of the email's content or headers covered by the DKIM signature, DKIM authentication will also fail. This leads to DMARC failure, even for originally authenticated messages, impacting deliverability, especially to strict mailbox providers like Gmail with p=reject policies.
Key findings
- DMARC's reliance on alignment: DMARC requires either SPF or DKIM to pass authentication and for the authenticated domain to align with the domain in the From header. Forwarding often disrupts this alignment. For a detailed breakdown of DMARC, SPF, and DKIM, refer to our simple guide.
- SPF breaks with forwarding: When an email is forwarded, the forwarding server's IP address becomes the new sending IP. Since this IP is usually not listed in the original sender's SPF record, SPF authentication for the forwarded message will fail. This is a common and expected outcome.
- DKIM can break or survive: DKIM relies on a cryptographic signature of the email's headers and body. If the forwarding server modifies any signed part (e.g., adds a footer, changes the subject, or alters certain headers), the DKIM signature will become invalid, leading to a DKIM failure. However, if the forwarding is transparent and makes no alterations to signed content, DKIM can technically survive.
- Addressing DMARC failures for forwarded emails: Solutions like SRS (Sender Rewriting Scheme) can be implemented by forwarding mail servers to rewrite the Return-Path to ensure SPF passes when an email is forwarded. This is outlined in articles such as the effects of email forwarding on DMARC from GoDMARC.
Key considerations
- Strict DMARC policies: A DMARC policy set to p=reject will cause emails that fail DMARC to be rejected. This is why forwarded emails often bounce from recipient mail servers, particularly from those with strong DMARC enforcement like Gmail. This is especially relevant when considering stricter DMARC policies and G Suite forwarding.
- Postmaster tools: Mailbox providers like Google offer Postmaster Tools to senders, providing metrics on email deliverability, including DMARC pass/fail rates. These tools are crucial for monitoring and diagnosing authentication issues arising from forwarding.
- Intermediary server alterations: Documentation often points out that intermediary servers (including those used for forwarding) frequently modify email content or headers. These modifications break the cryptographic validity of DKIM, even if the sender has correctly signed their emails.
Documentation from GoDMARC explains that email forwarding affects DMARC due to its reliance on SPF and DKIM for authentication. When an email is forwarded, the original sender's SPF record may no longer align, and the DKIM signature can be broken if content is altered.
Documentation from Medium highlights that forwarded emails commonly fail DKIM checks because intermediate servers often alter the email's content or headers. This modification breaks the original cryptographic signature, leading to authentication failure.
