The Exchange Team released the quarterly Cumulative Updates for Exchange Server 2019 and Exchange 2016. Biggest change for both editions is support for Anti-Malware Scan Interface (AMSI) integration, available on Windows Server 2016 and Windows Server 2019. It allows real-time scanning of HTTP payloads, blocking known malicious content before it reaches Exchange.

Links to the updates as well as a description of changes and fixes are described below. The column Schema and AD indicate if the CU contains Schema (/PrepareSchema) and Active Directory (PrepareAD) changes compared to the previous CU.

Version	Build	KB	Download	UMLP	Schema	AD
Exchange 2019 CU10	15.2.922.7	KB5003612	Download		Y	Y
Exchange 2016 CU21	15.1.2308.8	KB5003611	Download	UMLP	Y	Y

Exchange 2019 CU10 fixes:

• 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
• 5004617 TLS 1.2 is not set as default after you install Exchange 2019 with Edge Transport role
• 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
• 5004622 “Cannot Send Mail – Your mailbox is full” error when you use iPhone mail to send very large attachments
• 5004623 PrepareADSchema required because of Active Directory schema change

Exchange 2016 CU21 fixes:

• 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
• 5004622 “Cannot Send Mail – Your mailbox is full” error when you use iPhone mail to send very large attachments
• 5004623 PrepareADSchema required because of Active Directory schema change
• 5004629 No version updating after you install Exchange Server 2016

Notes:

• If these Cumulative Updates contain schema changes compared to the Cumulative Update you have deployed, you need to run Setup with /PrepareSchema. If they contain Active Directory changes, you need to run /PrepareAD. Alternatively, permissions permitting, you can let Setup perform this step. Consult the Exchange schema versions page for version number comparison.
• When upgrading from an n-2 or earlier version of Exchange, or an early version of the .NET Framework, consult Upgrade Paths for CU’s & .NET.
• Don’t forget to put the Exchange server in maintenance mode prior to updating. Regardless, setup will put the server in server-wide offline mode post-analysis, before making actual changes.
• When using Exchange hybrid deployments or Exchange Online Archiving (EOA), support requires you to trail at most one version (n-1).
• If you want to speed up the update process for systems without internet access, you can follow the procedure described here to disable publisher’s certificate revocation checking.
• Cumulative Updates can be installed directly; no need to install RTM prior to installing Cumulative Updates.
• Once upgraded, you can’t uninstall a Cumulative Update nor any of the installed Exchange server roles.
• The recommended upgrade order is internet-facing, non-internet-facing servers first, followed by Edge Transports.

Caution:

As for any update, I recommend to thoroughly test updates in a test environment prior to implementing them in production. When you lack such facilities, hold out a few days and monitor the comments on the original publication or forums for any issues.