Exchange Online is updating bulk email filtering for better accuracy, factoring in intermediaries and enhancing BCL scores, especially when CAUTH is set to None. Rollout begins early October 2024, with completion by late October. Admins should review logs and prepare for changes in bulk email management.
Applies to: Exchange Online · Microsoft Defender XDR
Source: mc.merill.net — data via Merill Fernando's open archive (MIT).