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IMPORTANT: This regularly scheduled cumulative update contains all the security fixes of the security updates in March and other previous security updates.

This update also includes new daylight saving time (DST) updates for Exchange Server 2016. For more information about DST, see Daylight Saving Time Help and Support Center.

Known issues in this cumulative update

  • In multidomain Active Directory forests in which Exchange is installed or has been prepared previously by using the /PrepareDomain option in Setup, this action must be completed after the /PrepareAD command for this cumulative update has been completed and the changes are replicated to all domains. Setup will try to run the /PrepareAD command during the first server installation. Installation will finish only if the user who initiated Setup has the appropriate permissions.

    • About the /PrepareDomain operation in multidomain:

      The /PrepareDomain operation automatically runs in the Active Directory domain in which the /PrepareAD command is run. However, it may be unable to update other domains in the forest. Therefore, a domain administrator should run the /PrepareDomain in other domains in the forest.

    • About the permission question:

      Because the /PrepareAD is triggered in Setup, if the user who initiates Setup isn't a member of Schema Admins and Enterprise Admins, the readiness check will fail, and you receive the following error messages.

      Error 1:

      The Active Directory schema isn't up-to-date, and this user account isn't a member of the 'Schema Admins' and/or 'Enterprise Admins' groups. For more informaion, visit:

      Error 2:

      Global updates need to be made to Active Directory, and this user account isn't a member of the 'Enterprise Admins'group. For more information, visit:

      To avoid the errors, either the user should join Schema Admins and Enterprise Admins groups or another user in Schema Admins and Enterprise Admins groups should manually run /PrepareAD for this Cumulative Update first. Then, the Exchange admin user can start Setup.

  • Autodiscover Event ID 1 occurs after you install Cumulative Update 14 for Exchange Server 2016. For more information, see KB 4532190.

  • "500 Unexpected Error" when trying to create a user mailbox in ECP. For more information, see KB 5001874.

Issues that this cumulative update fixes

This cumulative update also fixes the issues that are described in the following Microsoft Knowledge Base articles:

  • 5001183 Attachment is treated as bad zip file on Edge Transport server in Exchange Server 2019 and 2016

  • 5001184 EAC has no option to select the correct tenant for an Office 365 mailbox in Exchange Server 2019 and 2016

  • 5001185 EAC has no option to select an archive domain for cloud-based archive in Exchange Server 2019 and 2016

  • 5001186 Encoding of special characters isn't preserved which causes missing text in Outlook in Exchange Server 2019 and 2016

  • 5001188 Incorrect MRM properties stamped on mail item delivery when sending to multiple mailboxes on the same database in Exchange Server 2019 and 2016

  • 5001189 Mailbox Audit log searches and Outlook both tied to MaxHitsForFullTextIndexSearches in Exchange Server 2019 and 2016

  • 5001190 MonitoringGroup can't control the placement of CAS monitoring mailboxes in Exchange Server 2019 and 2016

  • 5001192 Microsoft Teams fails to show calendar due to Autodiscover v2 isn't site aware in Exchange Server 2019 and 2016

  • 5001193 New health mailboxes for databases are created every time Exchange Health Manager service is restarted

  • 5001194 RFC certificate timestamp validation in Exchange Server 2019 and 2016

  • 5001195 UPN specified when creating mailbox is overwritten automatically causing login failures in Exchange Server 2019 and 2016

  • 4583558 PDF preview function in OWA leads to download action unexpectedly

Get Cumulative Update 20 for Exchange Server 2016

Download Center

Download Download Cumulative Update 20 for Exchange Server 2016 (KB4602569) now

Download Download Exchange Server 2016 CU20 UM Language Packs now


  • The Cumulative Update 20 package can be used to run a new installation of Exchange Server 2016 or to upgrade an existing Exchange Server 2016 installation to Cumulative Update 20.

  • You don't have to install any previously released Exchange Server 2016 cumulative updates or service packs before you install Cumulative Update 20.

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