Why are DKIM validations failing intermittently with Office365?
Summary
What email marketers say7Marketer opinions
Email marketer from StackExchange suggests that one way to find the issue is to investigate all the server hops that the mail passes through.
Email marketer from StackExchange responds that there could be issues relating to key rotation so you should verify the key is up to date.
Email marketer from SparkPost explains that problems with character encoding or unsupported characters in the email body can cause DKIM verification to fail, as it corrupts the signature. Always test email sending to diagnose this issue.
Email marketer from Reddit responds that old DNS setups might be failing to automatically update the DKIM records, and suggests checking the setup process to ensure that it is automated correctly.
Email marketer from EasyDMARC shares that issues with SPF alignment can sometimes indirectly cause DKIM failures. While DKIM itself might be configured correctly, DMARC policies can lead to failure if SPF records are misconfigured.
Email marketer from StackExchange suggests ensuring there are no other CNAME records set for the same host, as this can cause problems.
Email marketer from ValMail explains that DNS propagation delays can result in intermittent DKIM validation failures. It is important to verify DNS records using online tools and ensure that the correct DKIM TXT record is published and fully propagated.
What the experts say5Expert opinions
Expert from Spam Resource explains that a very common cause of DKIM problems are DNS record problems. These include: not waiting long enough after the DNS change, typo's in the records or DNS servers having issues.
Expert from Email Geeks explains that the 'n' tag in a DKIM CNAME record is for human-readable notes and is not used in the validation process.
Expert from Email Geeks shares that if DKIM validation fails for only some emails, the issue is more likely related to the mail body being modified in transit, rather than the DKIM key itself.
Expert from Email Geeks explains that failing close to 50% of DKIM validation often indicates a DNS issue, such as having two DNS servers, one with a valid key and one without.
Expert from Word to the Wise explains that sometimes enabling DKIM can expose existing issues with your sending practices or infrastructure, leading to increased visibility of failures that were previously masked. These can include inconsistent DNS records or email content manipulation.
What the documentation says3Technical articles
Documentation from Microsoft Docs explains that intermittent DKIM failures can occur if there are inconsistencies or propagation delays in your DNS records. Ensure that your DKIM records have fully propagated across all DNS servers.
Documentation from Microsoft Docs shares that one common cause of intermittent failures is incorrect configuration of the DKIM signing settings within Office 365. Double-check the signing policy and ensure it is enabled for the correct domains and users.
Documentation from Microsoft Docs explains that DKIM failures happen intermittently if email content is altered in transit by a middle server. This alteration invalidates the DKIM signature, so it is necessary to investigate any potential mail flow issues, or ensure that email is not being altered by third-party programs.