New Limit on M365 Mail Starts May 2025

Exchange Online will enforce a tenant-level limit on the number of external recipients contacted every 24 hours, starting in May 2025. Exchange Online already enforces a similar cap per mailbox, but the tenant-level cap could disrupt mail for some organizations that use Exchange Online for customer service or billing. The limit is based on the number of user licenses purchased for the tenants starting at 10,000 external recipients for a tenant with a single license.  (See the nearby diagram.) For those caught by the limit, Microsoft proposes Azure Communication Services, its platform for custom applications that use chat, voice, and mail. Exchange Online is already offering previews of a paid service, High Volume Email for Microsoft 365, that is exempt from the cap. Exchange Online customers should expect further limits, and further ways to buy out of them. Trends for Exchange Online are explained in the Directions on Microsoft Business Applications Roadmap. Microsoft’s announcement and further discussion about The Tenant External Recipient Rate Limit (TERRL) are in the blog post and comments at “Introducing Exchange Online Tenant Outbound Email Limits” (Microsoft).