Microsoft Exchange Online Outage Disrupts Email Delivery in North America and Germany

Microsoft is actively investigating a widespread service disruption affecting the mail flow pipeline for Exchange Online customers in North America and Germany. The incident, tracked internally as EX1331830, was first acknowledged at 10:33 EDT after a surge of user reports on social media highlighted significant email delivery problems. Some affected users are encountering temporary SMTP deferral errors with the message, "The maximum number of concurrent connections per resource forest has exceeded a limit, closing transmission channel," while others receive "Connection was closed abruptly (SuspiciousRemoteServerError)" responses when attempting to transmit messages.

In an admin center service alert, Microsoft confirmed that users are experiencing substantial delays in sending and receiving email, with some messages remaining undelivered for over an hour. The company has classified the event as a formal incident, a designation typically reserved for critical service issues with measurable user impact. Engineers are currently aggregating customer reports from both regions to isolate the affected error messages, determine the full scope of disruption, and identify the root cause. Organizations relying on Exchange Online for business communications can run an SSL/TLS checker to verify their mail server configurations and rule out local connection issues while Microsoft works on a resolution.

The Exchange Online disruption adds to a string of Microsoft 365 incidents this year. In April, the company resolved intermittent mailbox access issues that had affected Outlook mobile and macOS users for weeks, alongside a separate outage that blocked access to mailboxes and calendars via Outlook on the web, Outlook desktop, and Exchange ActiveSync. More recently, on Monday, Microsoft addressed an incident preventing Teams and Office for the web users from opening files, as well as a separate issue that blocked customers from setting up multi-factor authentication or accessing the My Sign-Ins platform. As a precaution, IT teams should run a privacy checkup on their endpoint configurations to ensure authentication and connectivity dependencies remain stable during the ongoing outage. Microsoft has stated that updates will be provided as the investigation progresses, and this remains a developing story.