How to troubleshoot DKIM failures and which tools to use?

Email marketer from MXToolbox shares that they offer a DKIM record lookup tool and a DKIM authentication test, which can be used to check the validity of the DKIM record and the signature of a sample email, to assist with troubleshooting.

Email marketer from SparkPost explains that a common reason for DKIM invalidity is alteration of the email content between signing and delivery, which can be caused by forwarding services or email clients adding footers or disclaimers. They advise implementing proper content signing practices and regularly monitoring DKIM results.

Email marketer from Reddit suggests checking the raw email headers to understand the DKIM signing process and identify potential points of failure, also recommending using online tools to decode the headers and validate the DKIM signature.

Email marketer from Mailhardener recommends using online DKIM checkers, such as their own, to verify the DKIM signature of an email. They advise sending a test email to the checker address and reviewing the results to identify any errors in the DKIM configuration.

Email marketer from Valimail shares that common DKIM errors include DNS record syntax errors, incorrect key length, and the use of multiple DKIM records. They suggest regularly auditing DKIM configurations and using their online tools to validate DNS records.

Email marketer from StackOverflow advocates sending test emails to multiple email providers (Gmail, Yahoo, Hotmail) and analyzing the authentication results in the email headers to identify provider-specific DKIM issues. They emphasize using tools like `nslookup` or online DNS checkers to ensure the DKIM record is correctly published.

Marketer from Email Geeks argues that no mailbox provider is a perfect reference implementation of DKIM. A true reference implementation would likely break more often than what providers like Google consider valid, as perfect is the enemy of good.

Email marketer from EasyDMARC emphasizes that to prevent DKIM failures, it's crucial to generate strong DKIM keys, regularly rotate those keys, and implement DMARC to monitor and enforce email authentication policies. They promote using their DMARC monitoring platform to track DKIM performance.

Expert from Word to the Wise explains that forwarding services can sometimes alter email content, invalidating the DKIM signature. To troubleshoot, send test emails through various forwarding scenarios and examine the headers for DKIM pass/fail results. Consider using ARC (Authenticated Received Chain) to preserve authentication results through forwarding.

Expert from Email Geeks shares a hierarchy of checks for troubleshooting DKIM failures: 1. Check the public key's validity using tools like xnnd.com to look for intermittent failures. 2. Run an auth test using tools like kbxscore.com to see if everything passes. 3. Check via sending to Gmail and Hotmail accounts, noting that Gmail is forgiving while Microsoft is more sensitive to DNS issues. Microsoft may also have DKIM failures due to encoding issues.

Expert from Spam Resource explains that a frequent problem is a mismatch between the DKIM selector used in the email header and the one specified in the DNS record. Ensure they are identical. Use online DKIM checkers to validate the entire signature.

Expert from Email Geeks suggests that Gmail could be considered the de facto standard for DKIM implementation, given its large user base, though not necessarily 'exactly correct'.

Expert from Spam Resource explains that a common cause of DKIM failures is an incorrect DNS record. Check the syntax, ensure it's published correctly, and verify the selector matches the one used for signing. Tools like `dig` can help diagnose DNS issues.

Documentation from dmarcian explains that DKIM failures often stem from incorrect DNS configuration, modifications to the email body during transit (such as by a forwarding service), or issues with the signing server. They recommend using their DKIM Inspector tool and DMARC monitoring services to identify and resolve these issues.

Documentation from Google Workspace Admin Help explains that to troubleshoot DKIM failures, administrators should verify that the DKIM record is properly configured in the DNS settings, ensure the selector used in the DKIM record matches the selector used when signing the email, and check for any modifications to the email content during transit that could invalidate the DKIM signature. Tools like Google Admin Toolbox's Messageheader tool can assist in analyzing email headers for DKIM status.

Documentation from Microsoft Learn explains that troubleshooting DKIM failures in Microsoft 365 involves verifying the DKIM signing configuration, ensuring the correct public key is published in DNS, and using message trace logs to identify points of failure. They advise using the Test-DkimSignature cmdlet in Exchange Online PowerShell to validate DKIM signatures.