Summary
Email forwarding introduces significant challenges to email authentication. SPF fails because the forwarding server's IP address differs from the authorized IP in the original sender's SPF record. DKIM can be broken if the forwarding process modifies the email content, invalidating the signature. While DMARC only requires one of SPF or DKIM to pass, forwarding often breaks both, leading to DMARC failures and potential delivery issues like rejection or spam classification. ARC (Authenticated Received Chain) is a potential solution that preserves authentication results across multiple hops. In general, standard email forwarding practices are inherently incompatible with SPF and create challenges for maintaining email deliverability.
Key findings
- SPF Failure: Forwarding inevitably causes SPF to fail due to the change in the sending server's IP address, which no longer matches the original sender's SPF record.
- DKIM Breakage: Forwarding can alter the email's content, invalidating the DKIM signature and leading to authentication failure.
- DMARC Failure: If both SPF and DKIM fail due to forwarding, DMARC authentication will fail, potentially resulting in email rejection or spam classification.
- ARC as Mitigation: ARC (Authenticated Received Chain) helps to preserve authentication results across forwarding hops, mitigating the negative impacts of forwarding on SPF, DKIM, and DMARC.
Key considerations
- ARC Implementation: Consider implementing ARC to improve authentication persistence across forwarding hops and enhance email deliverability.
- DMARC Policy Adjustment: Carefully configure your DMARC policy to balance security with the potential for legitimate forwarded emails to be rejected.
- Content Alteration Prevention: Minimize content alterations during forwarding to preserve DKIM signatures and prevent authentication failures.
- Alternative Methods: Explore alternatives to forwarding, such as sharing links or attachments, to avoid breaking SPF and DKIM.
What email marketers say
12 marketer opinions
Email forwarding significantly impacts SPF, DKIM, and DMARC validation. Forwarding often causes SPF to fail because the IP address of the forwarding server differs from the IP authorized by the original sender's SPF record. If the forwarding process also breaks DKIM (e.g., by altering the message content), DMARC will likely fail, potentially leading to email rejection or spam classification. While DMARC only needs one of SPF or DKIM to pass, forwarding can invalidate both. Solutions like ARC aim to preserve authentication results across forwarding hops.
Key opinions
- SPF Failure: Forwarding changes the sending server's IP, causing SPF to fail as the new IP is not authorized in the original sender's SPF record.
- DKIM Breakage: Forwarding can alter message content, invalidating DKIM signatures and leading to authentication failure.
- DMARC Impact: If both SPF and DKIM fail due to forwarding, DMARC authentication will fail, potentially resulting in email rejection or spam classification based on the sender's DMARC policy.
- DMARC Reliance: While DMARC requires only SPF or DKIM to pass, forwarding often breaks both, leading to deliverability issues.
- No Bounce, Spoofing: Lack of bounces when rejected emails from DMARC could be a sign of spoofing
Key considerations
- ARC Implementation: Consider implementing ARC to preserve authentication results across forwarding hops, mitigating the negative impact on SPF, DKIM, and DMARC.
- DMARC Policy: Understand and carefully configure your DMARC policy to balance security with the potential for legitimate emails to be rejected due to forwarding.
- DKIM Hardening: Ensure DKIM is robustly implemented to minimize the risk of breakage during forwarding, such as by avoiding alterations to the message body.
- Forwarding Practices: Educate users about the impact of forwarding on email authentication and explore alternative methods, such as sharing links or attachments, to avoid breaking SPF and DKIM.
Marketer view
Email marketer from Reddit explains that if forwarding breaks both SPF and DKIM, DMARC will likely fail, potentially causing emails to be rejected or marked as spam, depending on the DMARC policy set by the sending domain.
27 Apr 2023 - Reddit
Marketer view
Email marketer from StackOverflow highlights that SPF fails upon forwarding because the IP address of the forwarding server differs from the IP authorized by the original domain's SPF record. The email now originates from a server not permitted by the sender's SPF policy.
16 Mar 2022 - StackOverflow
What the experts say
2 expert opinions
Email forwarding disrupts SPF validation because receiving servers check the IP address against the original sender's SPF record. The forwarding server's IP, which is different, leads to SPF failure. Authenticated Received Chain (ARC) is a solution that preserves authentication results across multiple hops, helping to address issues caused by forwarding with SPF, DKIM, and DMARC.
Key opinions
- SPF Failure Mechanism: SPF fails because the forwarding server's IP doesn't match the IPs authorized in the original sender's SPF record.
- ARC as a Solution: ARC helps maintain authentication results when emails are forwarded, mitigating issues with SPF, DKIM, and DMARC.
Key considerations
- ARC Implementation: Consider implementing ARC to preserve authentication across forwarding hops.
- Address SPF Issues: Understand that SPF will inherently fail on forwarded emails without solutions like ARC.
Expert view
Expert from Word to the Wise shares information about Authenticated Received Chain (ARC), explaining that ARC preserves email authentication results across multiple hops. ARC helps maintain authentication when forwarding occurs and helps solve issues forwarding causes with SPF, DKIM, and DMARC.
6 Jun 2025 - Word to the Wise
Expert view
Expert from SpamResource explains that SPF failures in forwarded emails are due to the receiving mail server checking the IP address against the SPF record of the original sender. When an email is forwarded, the IP address of the forwarding server is used, which does not match the authorized IPs in the SPF record, causing a failure.
3 Jul 2021 - SpamResource
What the documentation says
5 technical articles
Email forwarding commonly disrupts SPF, DKIM, and DMARC. SPF fails because the forwarding server's IP doesn't match the original sender's authorized IPs. DKIM can break if the forwarding server modifies the email content, invalidating the signature. DMARC, which relies on SPF and DKIM alignment, can fail, potentially causing delivery issues. Standard email forwarding is inherently incompatible with SPF.
Key findings
- SPF Incompatibility: Standard email forwarding is incompatible with SPF due to the change in sending server IP address.
- DKIM Breakage on Modification: DKIM signatures are invalidated if forwarding servers modify the email content (e.g., adding disclaimers).
- DMARC Failure Risk: Forwarding invalidates SPF, and often DKIM, leading to DMARC failures and potential delivery issues.
- Unauthorized Source: Forwarded emails can be flagged as unauthorized because the IP address no longer matches the original sending domain.
Key considerations
- Content Modification: Avoid modifying email content during forwarding to preserve DKIM signatures.
- Alternative methods: Consider using alternative methods of sharing information, such as sharing links to avoid impacting SPF, DKIM and DMARC validation.
- DMARC Rejection: Consider if your email policies are flagging forwarded emails as spam when they are legitimate.
Technical article
Documentation from Google explains that forwarding can disrupt SPF and DKIM authentication. Because forwarded messages come from a different server, SPF checks might fail. If the forwarding process alters the message content, DKIM could also fail, potentially causing the messages to be flagged as spam.
6 Oct 2022 - Google
Technical article
Documentation from RFC Editor explains that standard email forwarding is incompatible with SPF. SPF authenticates the sender based on the IP address of the sending server, which changes when an email is forwarded to a different server.
24 May 2022 - RFC Editor
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