Microsoft Exchange Online Outage Hits Mail Flow in North America and Germany
Microsoft is investigating a widespread Exchange Online outage disrupting mail flow for customers in North America and Germany. Users face significant sending and receiving delays with some messages undelivered for over an hour while engineers seek the root cause.
As of June 3, incident EX1331830 remains active and unresolved, affecting expanded regions including APAC and Europe. Microsoft is evaluating targeted service infrastructure resets as potential mitigation and analyzing mail queue backlogs for root cause.
Incident tracked as EX1331830. Microsoft first acknowledged this incident at 10:33 EDT. It began investigating reports from users on social media at that time.
The company has classified this service outage as an incident. This classification typically applies to critical service issues with noticeable user impact.
Some affected users are seeing temporary SMTP deferral errors stating "The maximum number of concurrent connections per resource forest has exceeded a limit, closing transmission channel."
Specific error messages reported. Some affected users are seeing temporary SMTP deferral errors stating "The maximum number of concurrent connections per resource forest has exceeded a limit, closing transmission channel." Others see "Connection was closed abruptly (SuspiciousRemoteServerError)" messages.
These ongoing issues are affecting Exchange Online users trying to send or access their emails. This is resulting in extensive delays or failures.
Extent of email delivery impact. Users are experiencing significant delays in sending and receiving email messages. Some email messages are remaining undelivered for over an hour, according to the company.
Microsoft said its engineers are currently reviewing reports to discover the root cause. The company issued the details in an admin center service alert.
Review of regional customer reports. The company is reviewing additional reports from customers in the North America and Germany regions. This work aims to further its understanding of the current impact scenario, isolate error messages affected users are receiving, and determine next troubleshooting steps.
In April Microsoft resolved Exchange Online mailbox access issues that had intermittently affected Outlook mobile and macOS users for weeks. It also resolved an Exchange Online outage that prevented users from accessing mailboxes and calendars via Outlook on the web, Outlook desktop, Exchange ActiveSync, and other Exchange Online connection protocols.
More recently on Monday it addressed an outage that prevented Teams and Office for the web users from opening files. It also handled an incident that prevented customers from setting up multi-factor authentication or accessing the My Sign-Ins platform.
EXPERT TAKE
Admins should check the Microsoft 365 admin center service alert for EX1331830 and prepare for potential SMTP retry configurations during the ongoing incident.
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