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Summary

When sending emails, encountering a DKIM permerror (bad sig) specifically on Yahoo Mail, while other mail services like Gmail validate the signature successfully, can be a perplexing issue. This specific error indicates that Yahoo Mail's servers are unable to verify the digital signature embedded in your email, suggesting a permanent problem with how the email was signed or how Yahoo processes the signature. The challenge often lies in pinpointing why Yahoo's validation differs from other major providers.

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What email marketers say

Email marketers often find themselves in a challenging position when a specific receiving domain, such as Yahoo Mail, flags their emails with a DKIM permerror (bad sig), even when other services validate the signature without issue. This discrepancy can be particularly frustrating after significant changes to email infrastructure, as it implies a unique interpretation or stricter enforcement of DKIM standards by Yahoo.

Marketer view

Email marketer from Email Geeks asks if others have encountered DKIM permerror (bad sig) on Yahoo, noting that other checkers show the DKIM as valid.

14 May 2019 - Email Geeks

Marketer view

Email marketer from Launchpad reports that emails sent with the same code pass DKIM for Google accounts but result in a 'dkim=permerror (bad sig)' for Yahoo accounts.

20 May 2019 - Launchpad

What the experts say

Email deliverability experts emphasize that while a DKIM permerror (bad sig) is a clear indicator of a signature mismatch, the root cause can be nuanced, especially when only one recipient (like Yahoo Mail) reports the failure. Their insights often point to subtle differences in how email is processed or how authentication standards are interpreted by various receiving systems.

Expert view

Email expert from Email Geeks observes that fast DNS TTLs, often set during changes, can worsen DNS-related DKIM failures like old key issues, emphasizing the need to verify DKIM TXT record TTLs are at least 300 seconds and ideally around 3600.

14 May 2019 - Email Geeks

Expert view

Email expert from SpamResource states that DKIM validation issues often stem from subtle changes to the email content or headers after the signature has been applied, such as a mailing list adding a footer.

10 Mar 2024 - SpamResource

What the documentation says

Technical documentation on DKIM provides the foundational understanding of how signatures are created and verified. A permerror (bad sig) signifies a permanent, unrecoverable failure in this verification process. While the documentation outlines the standard, real-world implementations by major mail providers like Yahoo can introduce subtle variations or stricter interpretations that lead to specific failures.

Technical article

RFC 6376 (DomainKeys Identified Mail (DKIM) Signatures) outlines that a 'permerror (bad sig)' indicates a permanent failure in signature verification, meaning the computed hash of the message does not match the signed hash provided.

22 Sep 2011 - RFC 6376

Technical article

The OpenDKIM documentation frequently highlights that common causes of 'bad sig' include message modification in transit, incorrect canonicalization methods, or issues with the private key used for signing.

15 Feb 2023 - OpenDKIM Documentation

4 resources

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