Why are emails being marked as spam when they're forwarded to Gmail addresses?

Summary

Emails being marked as spam when forwarded to Gmail addresses is a common and often perplexing issue for senders. Even if you do not directly send to Gmail, your emails can still end up in Gmail's spam folder due to forwarding by other mailbox providers. This scenario primarily arises because the forwarding process can break or alter crucial email authentication mechanisms like SPF, DKIM, and DMARC, making the forwarded messages appear suspicious to Gmail's sophisticated spam filters. Your sender reputation at Gmail can be negatively impacted, even if your direct sending practices are pristine.

What email marketers say

Email marketers often encounter unexpected spam placement, even when they believe their direct sending practices are sound. The issue of forwarded emails going to Gmail spam can be particularly frustrating because it's outside their direct control. Marketers typically focus on their own sending infrastructure and list hygiene, but the nuances of how other mailbox providers handle forwarded mail to Gmail can significantly impact their sender reputation, leading to confusion and deliverability challenges. This highlights the importance of a holistic approach to email deliverability that extends beyond direct sending.

Marketer view

Marketer from Email Geeks suggests that the volume of forwarded email, even if not directly sent to Gmail, can significantly impact spam placement. If a large number of emails are being forwarded and subsequently marked as spam, it contributes to a negative reputation. They emphasize that marketers need to be aware that indirect mail streams can still affect their overall deliverability metrics with major mailbox providers. The issue isn't just about direct sending but also about how your emails are handled downstream by other providers.

10 Nov 2024 - Email Geeks

Marketer view

Marketer from Quora notes that Gmail's algorithms are complex when determining spam, suggesting that user behavior and engagement play a huge role. Even if an email is legitimate, consistent negative feedback or low engagement, regardless of how it arrived, can lead to spam placement. They highlight the challenge of understanding why specific emails are marked as spam, especially when the sender has taken all traditional deliverability precautions. The black box nature of spam filters can be a major hurdle.

15 Oct 2024 - Quora

What the experts say

Email deliverability experts highlight that the problem of forwarded emails being marked as spam by Gmail is fundamentally rooted in how email authentication protocols interact with the forwarding process. Forwarding can alter the original message path, breaking SPF and DKIM validation. This doesn't just make the forwarded email look suspicious; it actively undermines the sender's domain reputation with Gmail, even for emails they don't directly send to Gmail users. Experts stress the importance of understanding these technical nuances to mitigate unintended spam placement.

Expert view

Expert from Email Geeks suggests that not mailing specific domains like Gmail, while seemingly strategic, can actually be a major red flag for mailbox providers and indicate likely abusive activities. This can negatively impact overall sender reputation, even if mail is only arriving indirectly via forwarding. They argue that a sender's reputation is built through all mail streams, direct or indirect. Avoiding a large recipient base like Gmail may suggest an attempt to evade scrutiny, which can backfire when mail is eventually seen there through other channels.

09 Nov 2024 - Email Geeks

Expert view

Deliverability expert from SpamResource explains that SPF validation is particularly vulnerable to breakage during forwarding. When an email is forwarded, the `Return-Path` header often changes to that of the forwarding server, which will not match the original sender's SPF record. This mismatch immediately triggers a softfail or hardfail, leading to increased spam scoring. They emphasize that because SPF checks the envelope sender, a change in the sending path by a forwarding server is almost guaranteed to invalidate the original SPF alignment, signaling to receiving mail servers like Gmail that the message might not be legitimate.

18 Oct 2024 - SpamResource

What the documentation says

Official email documentation and standards provide the foundational understanding of why forwarded emails encounter deliverability issues. These documents describe how email authentication protocols SPF, DKIM, and DMARC are designed to verify sender identity. When an email is forwarded, the technical path and sometimes the content are altered, fundamentally challenging these authentication checks. This can lead to a state where the email, despite originating from a legitimate sender, fails to verify its authenticity upon reaching the final destination like Gmail, resulting in spam placement. Understanding these underlying mechanisms is key to diagnosing and potentially mitigating such issues.

Technical article

RFC 7208 on SPF explains that when an email is relayed by a forwarding server that is not authorized by the original sender's SPF record, the SPF authentication will fail. This is a deliberate design choice to prevent unauthorized sending. It clarifies that SPF is designed to check the IP address of the immediate sender against the domain in the Mail From header, which is why forwarding often breaks its alignment.

01 Apr 2014 - RFC 7208 (SPF)

Technical article

RFC 6376 on DKIM specifies that any modification to the signed parts of an email message, whether headers or body, after the DKIM signature has been applied, will invalidate that signature. This includes changes introduced by forwarding servers. It details how DKIM ensures message integrity and authenticity, making it clear why common forwarding practices, such as adding footers or modifying content, can lead to authentication failures.

01 Sep 2011 - RFC 6376 (DKIM)

12 resources

The following resources offer further insights into email deliverability and why emails, particularly forwarded ones, might land in spam.