An Exchange Online issue is disrupting email access for mobile Outlook users with Hybrid Modern Authentication. The tech giant has now found a solution, but this is far from the first time Outlook has experienced problems this year.
The problems with Outlook in 2025 continue to pile up. There was a global outage in March, a DNS misconfiguration until July, and a month earlier, the classic Outlook crashed when starting a mail message.
Problem affects mobile users
The current outage, registered under EX1137017 in the Microsoft 365 Admin Center, was caused by a recent update. This change was intended to improve the efficiency of mailbox synchronizations, but ironically causes significant delays for affected customers.
Outlook users on mobile devices have been experiencing problems for a week. Some mailboxes are crashing, preventing users from accessing email and calendars. “Some users may be unable to send or receive email through the Outlook app on their device,” Microsoft confirms in the service alert.
Technical cause identified
When a normal temporary malfunction occurs, an exception is now generated for a subset of users. This puts the synchronization task for emails in quarantine with a 12-hour wait time.
Microsoft employees have now rolled out a fix that ensures that synchronizations no longer end up in such a long quarantine. An earlier configuration change that would change the delay interval to one hour proved unsuccessful.
Simultaneous Teams issue
In addition to the Exchange Online issues, Microsoft is also investigating a Teams incident (TM1134507). Users are seeing blank screens and experiencing crashes during meetings when using the desktop app. This issue may affect users with Intel driver version 32.0.101.69xx.
As a temporary workaround, Microsoft advises affected customers to use the web version of Teams until the issue is resolved.
Microsoft has not yet disclosed which regions or how many customers are affected by the current Exchange Online issues. The incident is classified as a disruption, indicating a noticeable impact on users.
The technical details show that even well-intentioned optimizations can have unexpected side effects in an ecosystem as complex as Exchange Online. The question is whether the trend of Outlook issues will finally start to subside after this.
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