Microsoft Investigates Exchange Online Outage Affecting Outlook Email and Authentication

Microsoft is investigating a widespread Exchange Online outage that is causing authentication errors, email delays, and message delivery failures for customers using Microsoft 365 and Outlook.

The incident, tracked as EX1464935, was first reported at approximately 5:30 p.m. UTC. Reports of Microsoft 365 and Outlook problems have also surfaced on Reddit, user forums, and social media.

According to the outage-tracking service Downdetector, tens of thousands of Exchange Online users have reported problems sending and receiving email through Outlook, as well as difficulties accessing the Exchange Online service.

Exchange Online outage symptoms

Microsoft says customers affected by the incident may experience the following problems:

• Delays or failures when sending or receiving email messages.
• Authentication errors when accessing Exchange Online services.
• Difficulty accessing or completing tasks in the Exchange admin center.
• Intermittent failures affecting mailbox operations and email delivery workflows.

Microsoft has not yet confirmed which regions are affected. The company has classified the issue as an incident, a designation generally used for significant service disruptions that affect a large number of customers.

In its latest update to the Microsoft 365 admin center, Microsoft said it had identified a common failure pattern affecting Exchange Online requests associated with authentication and protocol connectivity.

“We have identified a common failure pattern across affected Exchange Online requests related to authentication and protocol connectivity,” Microsoft said.

“We are analyzing service telemetry to identify the underlying impact source and verify potential remediation options. Additionally, we continue to assess the impact area and monitor additional impact scenarios.”

Recent Microsoft Exchange Online outages

Microsoft has dealt with multiple Exchange Online outages in recent months. In June, the company mitigated a widespread service disruption affecting mail flow pipelines for customers in North America, Asia-Pacific, and Europe.

In April, Microsoft resolved mailbox access problems that intermittently affected Outlook Mobile and Outlook for Mac users for several weeks. The company also addressed Exchange Online outages that prevented customers from accessing mailboxes through Outlook on the web, Outlook for Windows, Exchange ActiveSync, and other Exchange Online connectivity protocols.

Microsoft has not announced a final resolution for the current Exchange Online outage. Customers experiencing authentication errors or email delivery problems should monitor the Microsoft 365 service health dashboard for additional updates.

This is a developing story and will be updated as more information becomes available.

The overall prevention score can hide what happens after the initial access. If an attacker uses valid credentials, your defenses drop sharply.

Blue Report 2026 measures defense techniques by technology across 338 million simulations run in customer production environments.

Get the report