If you are in the situation where you are migrating from a non-Microsoft mail system (e.g. Domino Lotus Notes, Google) or a hosted Exchange platform you may be in the situation where you have set up AAD Connect before extending your Active Directory Schema to include the Microsoft Exchange attributes. This can cause problems when trying to update you AAD Connect configuration to include the Exchange Hybrid attributes, seeing the following behaviour, the Exchange Hybrid Deployment option being greyed out, when you try to update the settings:
This is caused by the fact that when you first set up AAD Connect it collects and analyses your Active Directory schema, and adds the available attributes to its database. If you make changes to your AD schema, such as installing Exchange, you need to refresh AAD Connect’s stored schema configuration.
This should also be done whenever you perform an update/upgrade to Exchange that requires a schema update as you may find that new features/updates that could affect Exchange Online may not work properly.
If you do not include the Exchange Hybrid options in your AAD Connect configuration at this point it will not include any Exchange attributes in the synchronisation and so none of your on-premises mailboxes will show as Mail Users in Exchange Online as you would expect.
Luckily, in the latest version of AAD Connect refreshing the schema configuration is super easy!
If you launch the AAD Connect configuration wizard (this is normally added as a shortcut to the desktop on install, but is also available in the start menu under the AAD Connect folder) one of the options on the launch screen is “Refresh directory schema”.
When you select this option, you will be asked to confirm your Azure AD Admin credentials, and which directories you want to update. It will then re-check your Active Directory schema and update the available features in AAD Connect.
After completing these steps, when you next launch the AAD Connect configuration wizard and select “Customize synchronization options” the Exchange Hybrid Deployment tick-box will no longer be greyed-out, and you can continue with your Hybrid Deployment.
If you have any questions or comments please either use the comments section below, Tweet me@MikeParker365 or via email firstname.lastname@example.org.