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Exchange Server 2016 CU23 Exchange Server 2016 CU23 ESU only Hotfix update

KB5066370

KB5066370: Hotfix update for Exchange Server 2016 CU23, September 2025. Hybrid online archiving resumes for on-premises mailboxes

In short

Restores automatic online archiving for some on-premises mailboxes in hybrid environments. This update is available only to organizations enrolled in Extended Security Updates.

Does it affect you? Applies to: Exchange Server 2016 CU23 servers at organizations enrolled in Extended Security Updates (ESU).

Build
15.1.2507.59
Servicing branch
CU23

For servers running Cumulative Update 23: each cumulative update gets its own update. Support for this version ended on October 14, 2025: Microsoft releases this update only to organizations enrolled in the Extended Security Update (ESU) program, not through Microsoft Update. The others should move to Exchange Server Subscription Edition. Which version am I on?

What changes

Fix 1 change

Online archiving

  • Items configured to move to an online archive are moved automatically again for affected on-premises users in hybrid environments.1
    Applies when the archive mailbox is in Exchange Online, the primary mailbox remains on-premises, and the dedicated Exchange Hybrid Application feature is enabled. The affected items have a retention tag configured as Move to Archive.

Technical details

Data sheet · Security · Downloads · Components Click to collapse or expand

Data sheet

Released
2025-09-08
Classification
Updates
Type
Cumulative update
Servicing branch
CU23
Replaces
KB5063223, KB5057653
Replaced by
KB5066369
VersionBuildChannel
2016 15.1.2507.59 General availability

Security

No vulnerabilities are listed for this update.

Sources

Updated
Cited passages from Microsoft's official notes (1)
  1. 1. Online archiving fails for on-premises users in hybrid environment support.microsoft.com
Checked automatically: 8 of 8 checks passed, 1 quoted passage · compared with Microsoft's page on Oct 20, 2026
  • Quotes found in the official pages: passed
  • Numbers found in the sources: passed
  • Vulnerabilities from the dossier only: passed
  • Links to allowed domains only: passed
  • Every official change covered: passed
  • Readable plain text: passed
  • Changes confirmed by the file list: passed
  • Sources agree: passed

A second AI read the text against the sources: correctness 5/5, clarity 5/5, completeness 5/5. How we work

Published by The Update Bureau. Written with AI from Microsoft's own documents, checked by rules and a second AI. How we work · Report a mistake