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This September 2021 cumulative update (CU) will install Exchange Emergency Mitigation (EM) service. This service is designed to help secure your servers that are running Microsoft Exchange Server by applying mitigations to address any potential threats against them. It uses the cloud-based Office Config Service (OCS) to check for and download available mitigations and to send diagnostic data to Microsoft. 

This CU has the following additional prerequisites:

Cumulative Update 11 for Microsoft Exchange Server 2019 was released on September 28, 2021. It includes fixes for nonsecurity issues and all previously released fixes for security and nonsecurity issues. These fixes will also be included in later cumulative updates for Exchange Server 2019

Known issues in this cumulative update

  • In multidomain Active Directory forests in which Exchange is installed or was 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 /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:

  • Autodiscover Event ID 1 occurs after you install Cumulative Update 3 for Exchange Server 2019. For more information, see KB 4532190.

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

  • "Cannot Send Mail - Your mailbox is full" error when you use iPhone mail to send very large attachments. For more information, see KB 5004622.

Issues that this cumulative update fixes

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

  • 5006980 Bad signature error using PerfView in Exchange Server 2019 and 2016 (KB5006980)

  • 5006982 On-premises Exchange queues back up because of incorrect default value (KB5006982)

  • 5006983 Exchange Server 2019 and 2016 certificates created during setup use SHA-1 hash (KB5006983)

  • 5006984 PrepareAD fails if Computers container or RODCs are renamed or moved in Exchange Server 2019 and 2016 (KB5006984)

  • 5006986 Opening an Outlook message from the desktop removes line spacing (KB5006986)

  • 5006988 Export of .pst file is unexpectedly triggered again in Exchange Server 2019 and 2016 (KB5006988)

  • 5006989 Accepted domains with wildcards for subdomains are not honored when Edge server maps AddressSpaces (KB5006989)

  • 5006990 Exchange CU installation fails after you configure fallback to use default character set (5006990)

  • 5006991 Mail quota warning messages no longer sent daily in Exchange Server 2019 (KB5006991)

  • 5006992 No room lists found when trying to add a room in OWA in Exchange Server 2019 or 2016 (KB5006992)

  • 5006993 Can't log on to OWA in Chrome if SSL is offloaded in Exchange Server 2019 and 2016 (KB5006993)

  • 5006994 BCC values not retained in Sent Items in a shared mailbox in Exchange Server 2019 and 2016 (5006994)

  • 5006995 Korean email messages display some recipients incorrectly in Exchange Server 2019 and 2016 (KB5006995)

  • 5006996 Export-AutoDiscoverConfig exposes admin password and does not work against domain controllers that require signing (KB5006997)

  • 5006997 Korean messages in OWA display "From" as "Start date" after you filter the list in Exchange Server 2019 and 2016

  • 5006999 "401" error and Outlook repeatedly prompts for credentials in Exchange Server 2019 (KB5006999)

  • 5007042 Error window appears when you view features in OWA Virtual Directory (KB5007042)

  • 5007043 Exchange Server SU updates Add/Remove Programs incorrectly (KB5007043)

  • 5007044 Start-MailboxAssistant not available in EMS in Exchange Server 2019 (KB5007044)

Get Cumulative Update 11 for Exchange Server 2019

Download Center

Download Download Cumulative Update 11 for Exchange Server 2019 (KB5005334) now

Volume Licensing Center

To get Cumulative Update 11 for Exchange Server 2019, go to Microsoft Volume Licensing Center.

Note The Cumulative Update 11 package can be used to run a new installation of Exchange Server 2019 or to upgrade an existing Exchange Server 2019 installation to Cumulative Update 11.

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Change history

 The following table summarizes some of the most important changes to this topic.



August 30, 2021

Added a "New feature in this cumulative update" section.

September 28, 2021

Added "Notice" at the top of the article.

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