Why do mailbox providers forward emails to a single Gmail account, causing DMARC failures?
Matthew Whittaker
Co-founder & CTO, Suped
Published 4 Aug 2025
Updated 19 Aug 2025
9 min read
Email forwarding is a common and convenient feature that allows users to receive emails sent to one address at a different inbox. This is incredibly useful for managing multiple email accounts, creating aliases, or ensuring continuity when changing email providers. However, for those of us deeply involved in email deliverability, forwarding often introduces complexities, particularly when it comes to DMARC authentication. I’ve seen countless scenarios where seemingly legitimate emails, once forwarded, fail DMARC checks, leading to delivery issues like messages being sent to spam folders or even outright rejected. It’s a frustrating experience to have your properly authenticated emails suddenly become unauthenticated simply because of an intermediary step.
The problem becomes even more pronounced when multiple email addresses from a specific mailbox provider (or ESP, as some might call it) are consistently forwarded to a single Gmail account. This particular pattern raises red flags and often results in a cascade of DMARC failures. Understanding why this happens requires a dive into the intricacies of email authentication protocols—SPF, DKIM, and DMARC—and how forwarding processes interact with them.
This article explores the core reasons behind these DMARC failures in forwarding scenarios, particularly when a single Gmail account becomes the final destination for multiple forwarded streams. I'll explain how forwarding breaks email authentication, discuss the various reasons why such consolidation might occur, and outline strategies to mitigate these issues and ensure your emails reach their intended inboxes.
When an email is forwarded, it doesn't simply get redirected. Instead, the intermediary server (the one performing the forwarding) receives the email and then re-sends it to the new recipient. This re-sending process often involves modifications to the email's envelope or headers, which can disrupt SPF and DKIM authentication. When these core authentication mechanisms break, the DMARC check for the original sending domain will fail, especially if the domain has a strict DMARC policy like p=reject or p=quarantine.
SPF (Sender Policy Framework) authenticates the sending server's IP address. When an email is forwarded, the IP address changes from the original sender's to the forwarding server's. Unless the forwarding server's IP is explicitly included in the original sender's SPF record, SPF authentication will fail. DKIM (DomainKeys Identified Mail) uses a cryptographic signature tied to the email's content and certain headers. Even minor modifications during forwarding, such as adding a footer, changing the subject line, or altering mailing list headers, will invalidate the DKIM signature, leading to a DKIM authentication failure. Both SPF and DKIM failures contribute to the DMARC failure, impacting deliverability.
How SPF breaks
IP address mismatch: The forwarding server’s IP isn't authorized by the original sender's SPF record.
Envelope sender rewrite: The forwarding process often changes the MFROM (Mail From) address, which SPF uses for validation, causing misalignment.
How DKIM breaks
Content modification: Any alteration to the email body or signed headers (like subject, from, to) by the forwarder invalidates the signature.
Header changes: Some forwarders add or remove headers, which can break the cryptographic hash.
DMARC (Domain-based Message Authentication, Reporting, and Conformance) relies on the successful authentication and alignment of either SPF or DKIM. If both fail due to forwarding, DMARC will mark the email as unauthenticated. This is a common challenge, as email forwarding was not originally designed with modern authentication protocols in mind. Many legacy forwarding systems simply pass the message along without any DMARC-aware mechanisms.
This behavior explains why DMARC often breaks forwarding by design. The system is doing exactly what it's supposed to do: flag emails that appear to be from a domain but don't pass the necessary authentication checks from their current sending path. The key takeaway is that when an email is forwarded, its path changes, and SPF and DKIM often cannot keep up unless specific measures are taken.
Why emails might be forwarded to a single Gmail account
The observation that emails from the same mailbox provider are all being forwarded to a single Gmail account, often with a username hinting at a redirection service (e.g., `redirectionforUOL@gmail.com`), is quite specific. This pattern can stem from several scenarios, some legitimate and others potentially problematic. Most commonly, this is set up by the individual email account owner, often a small business or a single person managing multiple aliases.
For instance, an organization might have various departmental email addresses (sales@example.com, info@example.com) that are all configured to forward to a single Gmail inbox for centralized management. This is a common practice for smaller entities that don't host their own robust email infrastructure. Alternatively, individuals might forward multiple personal aliases or legacy email addresses to their primary Gmail account for convenience, assuming that forwarding works seamlessly with all email systems.
However, if the forwarding is occurring without the explicit knowledge or consent of the original mailbox owner, or if it spans across many seemingly unrelated accounts, it could indicate something more concerning. This could suggest compromised mailboxes where an unauthorized party has set up forwarding rules to siphon off incoming communications. In such cases, the forwarded emails would still fail DMARC checks, but the root cause would be a security breach rather than a benign configuration. This is why it's critical to analyze DMARC reports closely.
Potential causes for suspicious forwarding
Compromised accounts: Malicious actors may set up forwarding rules to collect data from breached mailboxes.
Misconfigured catch-all domains: Less common but possible, where an administrator mistakenly forwards all incoming mail to one Gmail inbox.
Shadow IT or unapproved integrations: Unknown third-party services redirecting mail.
Impact of DMARC policies on forwarded emails
The DMARC policy set by the sending domain dictates how receiving mail servers should handle emails that fail authentication. These policies are specified in the DMARC record, which is published in the domain's DNS. The three main policies—p=none, p=quarantine, and p=reject—have different implications for forwarded emails that don't pass authentication.
When a domain has a p=reject policy, any email failing DMARC is simply not delivered to the recipient's inbox, and a bounce message is often sent back to the sender. This is why, in the case of emails forwarded to Gmail (or any mailbox provider), a DMARC failure leads to a bounce. The Gmail server recognizes the email as unauthenticated from your domain and, adhering to your `p=reject` policy, blocks it. This protects your domain from spoofing, but inadvertently punishes legitimate forwarded mail.
A p=quarantine policy, on the other hand, instructs receiving servers to place unauthenticated emails in the spam or junk folder. While less severe than outright rejection, it still impacts deliverability and user experience. A p=none policy is the most lenient, allowing unauthenticated emails to be delivered without penalty, primarily used for monitoring DMARC reports before enforcing stricter policies.
DMARC policy
Action on authentication failure
Impact on forwarded email
P=none
No action, email delivered.
Forwarded emails delivered, but you receive DMARC reports.
P=quarantine
Email goes to spam or junk.
Forwarded emails sent to spam or rejected by some providers.
P=reject
Email is blocked and bounces back to sender.
Forwarded emails are almost always rejected, causing bounces.
Troubleshooting and mitigation strategies
When facing DMARC failures due to email forwarding, particularly to aggregated Gmail accounts, it's crucial to adopt a systematic approach to identify and resolve the issue. The primary step is always to examine your DMARC reports. These reports provide invaluable insights into the authentication status of your emails, showing which messages are failing DMARC, the IP addresses from which they originated, and the receiving mailbox providers. By looking at the source IP addresses in your DMARC aggregate reports, you can confirm if the failures are indeed stemming from forwarding servers.
Example DMARC record with p=reject policy and reporting
For legitimate forwarding that you control, implementing a Sender Rewriting Scheme (SRS) can often resolve SPF failures. SRS rewrites the envelope sender address of a forwarded email so that it passes SPF checks at the final destination. While SRS addresses SPF, DKIM remains vulnerable to content modification during forwarding. If you are a mailbox provider, ensure your forwarding mechanisms don't alter email headers or content in ways that break DKIM signatures. For instance, Google advises against modifying MIME boundaries or the subject to preserve DKIM.
Best practices for forwarding and DMARC
Monitor DMARC reports: Regularly analyze your DMARC aggregate and forensic reports for authentication failures.
Implement SRS: Use Sender Rewriting Scheme on forwarding servers to ensure SPF passes.
Educate users: Inform users about how forwarding can affect email authentication and deliverability.
Contact mailbox provider: If you suspect suspicious activity or systemic forwarding issues, reach out to the mailbox provider's postmaster.
Views from the trenches
Best practices
Always review your DMARC reports to understand email authentication results and identify patterns, especially for forwarded emails.
Implement SRS (Sender Rewriting Scheme) on any mail server that forwards emails to ensure SPF passes.
Avoid making any content or header modifications when forwarding emails to preserve DKIM signatures.
For critical communications, consider direct delivery or alternative relay methods instead of relying on recipient-side forwarding.
Regularly check your domain's DMARC, SPF, and DKIM records for correct configuration and alignment.
Common pitfalls
Not monitoring DMARC reports, leading to unawareness of widespread authentication failures from forwarding.
Assuming that all email forwarding services are DMARC-aware and will maintain authentication.
Ignoring bounce messages that indicate DMARC policy violations for forwarded emails.
Having a strict DMARC policy (p=reject) without proper monitoring or understanding of its impact on forwarded mail.
Not communicating with mailbox providers about unusual forwarding patterns observed in DMARC reports.
Expert tips
Leverage DMARC forensic reports (RUF) for detailed insights into why specific emails are failing authentication.
If you are a mailbox provider, implement DMARC-compliant forwarding mechanisms like SRS or modify headers minimally.
Investigate any reports of multiple addresses forwarding to a single unfamiliar Gmail account; it might indicate a security issue.
When troubleshooting, verify both SPF and DKIM alignment, as DMARC requires at least one to pass.
Consider a DMARC p=quarantine policy initially to observe the impact before moving to p=reject for a stricter enforcement.
Expert view
Expert from Email Geeks says DMARC, by its very design, inherently breaks email forwarding. This is a common and expected behavior of the protocol.
November 11, 2019 - Email Geeks
Expert view
Expert from Email Geeks says many forwarding services only break SPF, while DKIM often survives, allowing the DMARC check to still pass successfully.
November 11, 2019 - Email Geeks
Ensuring deliverability with DMARC and forwarding
Navigating the complexities of email forwarding and DMARC authentication can be challenging, but a clear understanding of how these systems interact is key to ensuring successful email delivery. Forwarding inherently introduces points of failure for SPF and DKIM, which in turn leads to DMARC validation issues, especially with stricter policies like p=reject. The scenario of multiple addresses forwarding to a single Gmail account highlights both common user configurations and potential security concerns.
For domains implementing DMARC, particularly with a strong policy, continuous monitoring of DMARC reports is essential. These reports are your eyes and ears into your email ecosystem, revealing where authentication failures occur and providing the necessary data to troubleshoot. For situations where legitimate forwarding is causing issues, implementing technologies like SRS or ensuring that forwarding processes do not modify critical email headers can help preserve authentication.
Ultimately, maintaining good email deliverability means being proactive about authentication. By understanding how email forwarding impacts SPF, DKIM, and DMARC, and by regularly analyzing your DMARC data, you can safeguard your domain's reputation and ensure your messages consistently reach their intended recipients, regardless of their forwarding setups.
Gmail account for convenience, assuming that forwarding works seamlessly with all email systems.
Gmail (or any mailbox provider), a DMARC failure leads to a bounce. The Gmail server recognizes the email as unauthenticated from your domain and, adhering to your `p=reject` policy, blocks it. This protects your domain from spoofing, but inadvertently punishes legitimate forwarded mail.
