Resolved in KB5128895Known issue · Exchange Server update known issues · Exchange
ContentEngine deadlock because of missing Korean WordBreaker rule files
After you install the September 2026 Security Update for Microsoft Exchange, Exchange environments that process email messages that contain Korean language content might experience one or more of the following symptoms: Search results might be missing; Email delivery might be delayed; MAPI or Outlook clients might become unresponsive, stall, or disconnect.
36
Days since it was published · 8 Sep 2026
Other open issues in Exchange
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- Availability (free/busy) fails for delegated mailboxes in Exchange hybrid deployments using Graph API onlyOpen · Exchange Server update known issues
- showInAddressList property is out of sync with Microsoft ExchangeOpen · Microsoft Graph known issues
What changed
First observed 14 Oct 2026No field changes in the recorded history.
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