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

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: http://technet.microsoft.com/library(EXCHG.150)/ms.exch.setipreadiness.SchemaUpdateRequired.aspx.


      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: http://technet.microsoft.com/library(EXCHG.150)/ms.exch.setupreadiness.GlobalUpdateRequred.aspx.


      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.

  • "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:

  • 5004612 Message body not displayed in OWA if the message was added in Outlook to a new mailbox

  • 5004613 OutOfMemory exception when moving a public folder that has a large ICS sync state

  • 5004614 Korean text is garbled in calendar invitation to a user with a Chinese display name

  • 5004615 "InvalidOperationException" and Store Worker process crashes during mailbox move

  • 5004616 Changing the email address in EAC doesn't work in modern browsers

  • 5004618 MSExchangeMailboxAssistants 4999 Crash in ELCAssistant.InvokeInternalAssistant with System.NullReferenceException

  • 5004619 Mailbox creation through ECP fails after installing Exchange Server 2019 or 2016 April update

  • 5004629 No version updating after you install Exchange Server 2016

Get Cumulative Update 21 for Exchange Server 2016

Download Center

Download Download Cumulative Update 21 for Exchange Server 2016 (KB5003611) now

Download Download Exchange Server 2016 CU 21 UM Language Packs now
 

Notes

  • The Cumulative Update 21 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 21.

  • You don't have to install any previously released Exchange Server 2016 cumulative updates or service packs before you install Cumulative Update 21.

File information

File hash information

File name

SHA256 hash

ExchangeServer2016-x64-cu21.iso

403EFE9589709461FCC09B332894C4ED1F0D93414D9DBDCED1A0967727C47063

Change history

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

Date

Description

August 30, 2021

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

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