Removing the last Exchange server in a hybrid environment was announce more than 2 years ago with Exchange 2019 CU12 and Exchange 2016 CU23 (Released: 2022 H1 Cumulative Updates for Exchange Server) but finally I’m working with a customer that wants to do this, remove that last Exchange server in a hybrid environment.

This customer not in the process of decommissioning their datacenters yet, but they do want to decommission their last Exchange 2019 server (all their mailboxes are in Exchange Online). The Domain Controllers are still running on-premises, so the Exchange 2019 server is only used for management purposes (SMTP Relay is already moved elsewhere).

The first thing is to remove the Hybrid Configuration. I wrote about that in 2020, but the article is still valid: https://jaapwesselius.com/2020/12/15/remove-exchange-hybrid-configuration/.

The second step is to install the Exchange 2019 management tools. This can be on a Domain Controller or on a Management Server. To install the Exchange 2019 management tools, the Active Directory management tools, the Visual C++ Redistributable Package for Visual Studio 2012 and the IIS6 management tools must be installed first. Execute the following commands in an elevated PowerShell window:

PS C:\> Install-WindowsFeature rsat-adds,telnet-client
PS C:\> Enable-WindowsOptionalFeature -Online -FeatureName IIS-IIS6ManagementCompatibility, IIS-Metabase -All

The Exchange Management Shell is installed, when starting this it connects to an Exchange 2019 server. But when this server is not available the Exchange Management Shell fails. To work with Exchange PowerShell, open a regular Windows PowerShell and execute the following command:

PS C:\> Add-PSSnapin Microsoft.Exchange.Management.PowerShell.SnapIn

This uses the Exchange PowerShell module that’s installed on the management server, but it does not connect anywhere, and it does not use any RBAC configuration.
When using this, the following Exchange PowerShell commands are available:

• *-MailUser
• *-MailContact
• *-RemoteMailbox
• *-DistibutionGroup
• *-DistributionGroupMember
• *-EmailAddressPolicy
• Set-User and Get-User

When enabling an existing user account with a mailbox in Exchange Online, you can use the Get-User command and pipe it to the Enable-RemoteMailbox command, like this:

PS C:\ > Get-User JaapICT | Enable-RemoteMailbox -RemoteRoutingAddress JaapICT@contoso.mail.onmicrosoft.com

The Remote Mailbox will be created and all properties will be set correctly, including the email address conforming to the existing Email Address Policy. This is clearly visible when requesting the properties of the mailbox:

PS C:\> Get-RemoteMailbox -Identity JaapICT | select name -ExpandProperty EmailAddresses

Name               : JaapICT
AddressString      : C=NL;A= ;P=Corporation;O=Contoso;S=JaapICT;
ProxyAddressString : X400:C=NL;A= ;P=Corporation;O=Contoso;S=JaapICT;
Prefix             : X400
IsPrimaryAddress   : True
PrefixString       : X400

Name               : JaapICT
SmtpAddress        : JaapICT@Contoso.com
AddressString      : JaapICT@Contoso.com
ProxyAddressString : SMTP:JaapICT@Contoso.com
Prefix             : SMTP
IsPrimaryAddress   : True
PrefixString       : SMTP

Name               : JaapICT
SmtpAddress        : jaapict@Contoso.mail.onmicrosoft.com
AddressString      : jaapict@Contoso.mail.onmicrosoft.com
ProxyAddressString : smtp:jaapict@Contoso.mail.onmicrosoft.com
Prefix             : SMTP
IsPrimaryAddress   : False
PrefixString       : smtp

Now everything is working the last Exchange 2019 server can be removed. What I normally recommend is to disable all Exchange services on the server and leave it running for one or two weeks. If any issues arise it is easy to start the Exchange services again and fix the problem.

When nothing bad happens, you can remove the last Exchange server. After disabling the last mailboxes and removing the Mailbox Databases and Send Connectors, turn off the Exchange 2019 server. DO NOT UNINSTALL Exchange 2019, but shutdown the Exchange 2019 and remove the server. That is, delete the VM or reconfigure the bare metal server with something else, but DO NOT UNINSTALL the Exchange 2019 server. The management tools that are installed still use configuration settings in Active Directory.

From this moment on you must manage your recipient in Exchange Online using the on-premises management server where the Exchange Management Tools are installed (I say on-premises server, but this can also be a VM in Azure of course, as long as it is a domain joined server you are good).