Why does DKIM authentication sometimes fail with certain ISPs or receivers like Barracuda and Proofpoint?

DKIM authentication failures can stem from various factors. Security solutions like Barracuda and Proofpoint, often deployed in front of destination domains, may alter email content, impacting DKIM validity. Email forwarding, especially through mailing lists, modifies headers/body, thus invalidating the DKIM signature. Filters should verify DKIM before modifying the email body. Interoperability problems can arise from senders' practices violating protocol standards. Incorrect DNS configurations, character encoding issues, and problems with the DKIM key itself are other potential causes. ARC (Authenticated Received Chain) helps preserve authentication across hops if filters trust the results. DMARC policies are strict with DKIM and SPF alignment. The root cause of these problems need to be understood to ensure the best deliverability.

DKIM authentication failures can occur for several reasons, particularly when dealing with certain ISPs and receivers like Barracuda and Proofpoint. These failures often stem from modifications made to email content during transit by intermediaries, such as security gateways that alter URLs or add disclaimers. Incorrect DNS configuration, character encoding issues, and problems with the DKIM key itself also contribute. Forwarding emails, especially through mailing lists, can invalidate DKIM signatures due to header or body modifications. While a passing SPF record may sometimes mitigate the impact, it is crucial to ensure both SPF and DKIM pass for optimal deliverability, especially with stricter DMARC policies. Solutions like ARC (Authenticated Received Chain) and whitelisting sender IPs can help address these issues.

DKIM authentication failures can arise for various reasons, often pointing to underlying deliverability issues. A core principle is that filters should ideally verify DKIM signatures before modifying email bodies. Consistent failures with specific MTAs may signal interoperability problems, where certain sender practices, while acceptable to some, technically violate protocol standards. Email forwarding, particularly via mailing lists, commonly alters headers or bodies, thus invalidating DKIM signatures. Addressing these issues often involves understanding the root cause and working with ESP support. ARC (Authenticated Received Chain) is frequently proposed as a solution to preserve authentication results across multiple email hops, provided that filters reliably trust ARC results.

DKIM authentication failures can occur due to email forwarding, as the modification of message headers or the body by the forwarder invalidates the DKIM signature. ARC (Authenticated Received Chain) is crucial for preserving authentication results across multiple hops. DKIM failures can also lead to DMARC failures if the message doesn't align with SPF or other authentication mechanisms, potentially resulting in email rejection or being marked as spam. Changes made in transit, such as adding disclaimers or converting character encodings, also invalidate the DKIM signature, as outlined in the DKIM standard (RFC6376).