Starting July 1, 2026, A records for new Accepted Domains will use subdomains under mx.microsoft to support DNSSEC. Automation relying on mail.protection.outlook.com must update to use the List serviceConfigurationRecords Graph API for MX records. DNSSEC benefits apply automatically if enabled.
Applies to: Exchange Online
Source: mc.merill.net — data via Merill Fernando's open archive (MIT).