Troubleshooting 554 5.7.5 DMARC-related SMTP rejections

It's a bit of a cryptic error message, isn't it? Mail bouncing back with "554 5.7.5 Permanent error evaluating DMARC policy." Wondering how to troubleshoot that? Well, I covered exactly this in a recent Ask Al video for Valimail, which was inspired by this Reddit thread . If you're sending email (say, out of Google Workspace) and your recipients are protected by security gateways like Proofpoint…