After decommissioning the Resource Forest I still have an Exchange 2016 environment on-premises, but all my mailboxes are in Office 365. Users are provisioned in Active Directory, Remote Mailboxes are provisioned in Exchange 2016 and everything is synchronized to Office 365 using Azure AD Connect.
Do I still need an Exchange Hybrid Configuration? Unless there are plans to move resources back to Exchange on-premises there’s no need for a Hybrid Configuration. To stay in a supported configuration, an Exchange server on-premises is still needed for management purposes, but only Azure AD Connect is needed and not a full hybrid configuration.
Note. If you want to use the on-premises Exchange server for SMTP relay purposes you don’t need the Hybrid configuration either. Just make sure you have a SMTP Send Connector that points to Exchange Online Protection and you’re good.
Removing the Hybrid configuration consists of the following steps:
- Disable Autodiscover SCP in Exchange
- Remove the Hybrid Configuration from Active Directory
- Remove Connectors in Exchange Online
- Remove the Organization Sharing from Exchange Online
- Disable OAuth
Disable Autodiscover SCP in Exchange
When all Exchange resources are in Exchange Online you no longer need the on-premises Service Connection Points (SCP) for Autodiscover. But make sure you have the correct CNAME records for Autodiscover that point to Autodiscover.outlook.com.
To disable the SCP records in Active Directory, execute the following command in Exchange Management Shell:
Get-ClientAccessServer | Set-ClientAccessServer -AutoDiscoverServiceInternalUri $Null
Remove the Hybrid Configuration from Active Directory
Removing the Hybrid Configuration from Active Directory is just one PowerShell command in Exchange Management Shell:
There’s one pitfall here, this will also remove the outbound to Office 365 Send Connector from Exchange. If you want to keep SMTP relay from on-premises to your mailboxes in Exchange Online you have to manually recreate this connector (use yourdomain-com.mail.protection.outlook.com as a smarthost for this)
Remove Connectors in Exchange Online
In the Exchange Online Admin Center, remove the outbound SMTP connectors that point from Exchange Online to your on-premises Exchange organization. If you want to keep SMTP routing, keep the inbound SMTP connector, otherwise you can remove this as well.
Remove the Organization Sharing from Exchange Online
To remove the Hybrid Organization Sharing from Exchange Online navigate to Organization | Sharing in the Exchange Admin Center and remove the organization sharing.
Disable OAuth on-premises
When used before you can disable the OAuth configuration as well from Exchange on-premises and Exchange Online.
In Exchange on-premises Management Shell, execute the following command:
Get-intraOrganizationConnector | Set-IntraOrganizationConnector -Enabled $False
And to do this in Exchange Online Management Shell, execute the following (same) command:
Get-IntraorganizationConnector | Set-IntraOrganizationConnector -Enabled $False
These are the steps needed to remove the Hybrid Configuration from your Exchange environment.
Note. Microsoft recommends to leave the Exchange Hybrid option in Azure AD Connect.
In this blogpost I explained how to remove the Hybrid Configuration from your Exchange environment after you have moved all resources to Exchange Online.
The on-premises Exchange server is still needed for management purposes. After removing the Hybrid Configuration you can still manage your recipient Exchange Online using the on-premises Exchange server, all changes are replicated through Azure Active Directory.
Is that last Exchange server on-premises still needed? Yes, you need it for managing your recipients in Exchange Online. When you have Azure AD Connect running in your environment, the objects are managed in on-premises Active Directory. The source of authority is Active Directory. As long as Microsoft hasn’t fixed the source of authority problem, an Exchange server on-premises is still needed.