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Some users may be unable to access their Exchange Online mailboxes through most connection methods

Issue ID: EX920584
Services affected: Exchange Online
Status: Extended Recovery
Issue Type: Advisory
Start time: October 29, 2024 5:39 PM GMT+9

user impact
Users may be unable to access their Exchange Online mailboxes through most connection methods.

More info
Impacted connection methods include:

- Representational State Transfer (REST)
- Messaging API (MAPI)
- Exchange ActiveSync (EAS)
- Outlook on the web

Users who access the service through Internet Message Access Protocol (IMAP) aren't impacted by this event.

Scope of impact
Impact is specific to some users who are served through the affected infrastructure.

Root cause
Imbalanced resource utilization on an affected service dependency is causing impact.

current status
November 27, 2024 5:03 AM GMT+9
As we continue with our optimizations and to reduce the frequency of requests through the affected subset of service infrastructure, our testing of the Windows patch has validated that it will address the mailbox access problems and remediate the impact. We’re preparing the release of the Windows patch and we’re expecting that the deployment will have completed and remediated the impact by our next scheduled update.
Estimated time to resolve:
Our fix deployment timeline expectations that the Windows patch deployment will have completed by Tuesday, December 3, 2024.
Next update by:
Wednesday, December 4, 2024 6:00 AM GMT+9