Summary
Emails forwarded to Gmail face increased risk of being marked as spam due to a convergence of authentication failures, reputation issues, and Gmail's spam filtering mechanisms. The forwarding process often breaks SPF, DKIM, and DMARC authentication, hindering Gmail's ability to verify the original sender's identity. The reputation of both the original sender's domain and the forwarding server significantly influences deliverability. High volumes of forwarding, patterns resembling list bombing, and a lack of engagement with forwarded emails can trigger Gmail's spam filters. Strict DMARC policies can also cause forwarded emails to fail authentication. Properly configuring SPF records is crucial to allow forwarding.
Key findings
- Authentication Breakdown: Forwarding frequently disrupts SPF, DKIM, and DMARC authentication, causing verification failures.
- Reputation's Impact: The reputations of the sending and forwarding domains directly impact deliverability.
- Volume & Patterns Matter: High forwarding volumes or list-bombing patterns can trigger spam filters.
- SPF Configuration: Proper SPF configuration is essential for successful forwarding.
- Engagement Influence: Low engagement with forwarded emails may lead to spam filtering.
- DMARC's Role: Strict DMARC policies can cause forwarded emails to fail authentication.
- Forwarder is the Sender: Gmail sees the forwarder’s server as the sender.
Key considerations
- Authentication Practices: Ensure proper configuration of SPF, DKIM, and DMARC to prevent authentication failures during forwarding.
- Reputation Management: Proactively manage and monitor domain reputation to avoid blocklisting and ensure positive deliverability.
- Forwarding Behavior: Avoid excessive forwarding volumes and ensure legitimate forwarding practices to prevent triggering spam filters.
- DMARC Policy Adjustments: Carefully review and adjust DMARC policies to accommodate legitimate forwarding scenarios while maintaining security.
- Engagement Strategies: Implement strategies to encourage engagement with forwarded emails, signaling their value to Gmail.
- Monitor Authentication: Regularly monitor email authentication results and adjust configurations as needed to address any issues.
What email marketers say
12 marketer opinions
Emails forwarded to Gmail are often marked as spam due to a combination of factors related to authentication, reputation, and Gmail's spam filtering algorithms. Forwarding can break SPF, DKIM, and DMARC authentication, making it difficult for Gmail to verify the sender's identity. The reputation of the original sender's domain or the forwarding server also plays a crucial role, as a poor reputation increases the likelihood of emails being flagged as spam. Furthermore, high volumes of forwarded emails or patterns resembling list bombing attacks can trigger Gmail's spam filters.
Key opinions
- Authentication Failures: Forwarding can disrupt SPF, DKIM, and DMARC, leading to authentication failures at Gmail.
- Reputation Matters: The sender's and forwarder's domain reputation impacts deliverability.
- Volume and Patterns: High forwarding volumes or list bombing patterns can trigger spam filters.
- SPF Records: SPF records need to be configured at each domain, especially for forwarding.
- Gmail Thresholds: Gmail's thresholds for SPF/DKIM/TLS failures due to forwarding can cause issues.
Key considerations
- Authentication Configuration: Ensure SPF, DKIM, and DMARC are properly configured to minimize authentication failures during forwarding.
- Domain Reputation Management: Monitor and maintain a good domain reputation to prevent emails from being marked as spam.
- Forwarding Practices: Avoid high volumes of forwarding and ensure legitimate reasons for forwarding to prevent triggering spam filters.
- Understand Gmail's Filters: Gmail's spam filters are very complex, but keeping up to date with them will help maintain deliverability.
- DMARC Policy Considerations: If you are using DMARC ensure a relaxed policy to allow for emails to get forwarded.
Marketer view
Email marketer from Reddit shares that the receiving email server will be using it's spam detection algorithms based on the mail server IP address. This means that if a email from the past hasn't been recieved from that mail server before it could be marked as spam.
18 Aug 2023 - Reddit
Marketer view
Marketer from Email Geeks suggests high volumes of forwarded emails to Gmail could cause spam issues and questions the reasons for such forwarding.
29 Jan 2022 - Email Geeks
What the experts say
2 expert opinions
Emails are often marked as spam in Gmail when forwarded because the forwarding process can break authentication mechanisms like SPF and DKIM. Gmail relies on these to verify the sender's identity, and failures during forwarding increase the likelihood of emails being flagged as spam. Additionally, if the original sender's domain has a poor reputation or is on a blocklist, this negative reputation persists even when the email is forwarded, further contributing to deliverability issues.
Key opinions
- Authentication Breakage: Forwarding breaks authentication mechanisms (SPF, DKIM).
- Reputation Persistence: Original sender's negative reputation persists even when forwarded.
Key considerations
- Authentication Setup: Properly configure SPF and DKIM to minimize authentication breaks.
- Reputation Monitoring: Monitor domain reputation to avoid being blocklisted.
Expert view
Expert from Word to the Wise explains that forwarding can break authentication mechanisms like SPF and DKIM. Gmail relies on these to verify the sender's identity, and if they fail during forwarding, the email is more likely to be flagged as spam.
30 Apr 2023 - Word to the Wise
Expert view
Expert from Spam Resource notes that forwarded email can trigger spam filters if the original sender's domain is on a blocklist or has a poor reputation. Forwarding doesn't remove this negative reputation, and it can affect deliverability to Gmail.
28 Feb 2025 - Spam Resource
What the documentation says
4 technical articles
When emails are forwarded to Gmail, several factors contribute to them being marked as spam. Gmail identifies the forwarder's server as the sender, making the forwarder's IP reputation crucial. Authentication failures, often due to header alterations or strict DMARC policies, prevent Gmail from verifying the original sender's authenticity. Furthermore, a lack of engagement with forwarded emails can signal to Gmail that the recipient does not want these emails, leading to spam filtering.
Key findings
- Forwarder Reputation: Gmail sees the forwarder's server as the sender, so the forwarder's IP reputation is critical.
- Authentication Issues: Forwarding can alter headers, leading to authentication failures (SPF, DKIM, DMARC).
- DMARC Policies: Strict DMARC policies can cause forwarded emails to fail authentication.
- Engagement Signals: Lack of engagement (opens, clicks) with forwarded emails can lead to spam filtering.
Key considerations
- Authenticate Mail: Always use authenticated mail (SPF, DKIM, DMARC).
- Header Preservation: Ensure forwarding preserves vital email headers.
- DMARC Policy Review: Review DMARC policies to ensure they are not overly restrictive for legitimate forwarding scenarios.
- Engagement Strategies: Encourage engagement with forwarded emails to signal their value to Gmail.
Technical article
Documentation from DMARC.org explains that a strict DMARC policy (p=reject or p=quarantine) on the original sender's domain can cause forwarded emails to fail DMARC authentication at Gmail. This happens because the forwarded email's headers no longer align with the original sender's domain, leading Gmail to enforce the DMARC policy and potentially mark the email as spam or reject it.
11 Apr 2023 - DMARC.org
Technical article
Documentation from Google Workspace Admin Help shares that when emails are forwarded, Gmail sees the forwarder's server as the sender. If the forwarder's IP has a poor reputation or the original email failed authentication checks, Gmail might mark the forwarded email as spam. They suggest using authenticated mail.
5 Oct 2024 - Google Workspace Admin Help
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