compauth=fail: Microsoft Composite Authentication Explained
ID: 00eb8d17-00f6-5a1a-a93c-8d1026146f50
STIX ID: report--00eb8d17-00f6-5a1a-a93c-8d1026146f50
Feed Name: Security Boulevard
This blog post from PowerDMARC describes Microsoft’s Composite Authentication (compauth) layer used by Exchange Online Protection, explains compauth evaluation outcomes and reason codes, and outlines why compauth=fail has greater deliverability impact after Microsoft’s May 2025 sender enforcement. It provides step-by-step remediation: move DMARC away from p=none, ensure DKIM domain alignment and proper key management, configure custom return-paths for third-party ESPs, retain ARC for now while preparing for DKIM2, and use Microsoft 365 Spoof Intelligence overrides for false positives.
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