DKIM signature failures in Microsoft Office 365 are a multifaceted issue stemming from various sources, encompassing interoperability problems, DNS configuration errors, key management inadequacies, and procedural oversights. A potential lack of interoperability between Microsoft's DKIM implementation and older versions of OpenDKIM can lead to verification failures. Incorrect DNS settings, particularly after migration, are a common pitfall. The use of inadequate DKIM key sizes (below 2048 bits), coupled with a lack of regular key rotation, compromises security. Furthermore, mail flow configurations involving third-party security gateways, email forwarding practices, and DMARC misalignment can all contribute to these failures. Transport rules modifying emails and the presence of invalid or missing DKIM DNS records are also significant factors. Troubleshooting involves meticulous DNS record verification, proper key management, ensuring DMARC alignment, monitoring DKIM reports, and adhering to established DKIM standards.