Dealing with a failing DMARC email authentication protocol involves a multi-faceted approach encompassing monitoring, diagnosis, and remediation. Initially, implement a DMARC reporting tool to collect and analyze reports that identify failing email sources and causes, such as SPF alignment issues, DKIM signature failures, or unauthorized sending sources. Troubleshoot by checking SPF and DKIM records for accuracy and alignment, and audit email sending practices to identify legitimate sources. Resolve issues by configuring SPF and DKIM correctly, progressively tightening DMARC policies, and validating SPF records. For bulk senders, proper authentication alignment is crucial to meet requirements from Yahoo and Google. Internal systems and third-party vendors must be properly configured with SPF/DKIM. The initial DMARC policy (p=none) won't impact deliverability, but transitioning to stricter policies (p=quarantine or p=reject) requires careful monitoring and analysis to ensure legitimate mail is authenticating properly. Engaging a DMARC service provider can aid in this process. Tools such as aboutmy.email can assist in diagnosing issues. Failures indicate the email isn't authenticated as you, but as your ESP. It is critical to identify the source of the failing email stream and investigate the authentication method used by the sending server.