In Exclaimer, you want to use Dynamic Distribution Groups to specify signature conditions that determine when a signature must be applied for specific users. Even though the data has been synchronized in Exclaimer, the Dynamic Distribution Groups are still not available.
Dynamic Distribution Groups or details of users who are members of the Dynamic Distribution Groups cannot be synchronized from the Microsoft Graph API - this is where Exclaimer synchronizes the Azure Active Directory data from.
When you apply a signature, you can define a query based on the Active Directory user attributes. For example, you can define a signature for all users within a given department or who are based at a certain office and so on. You can also define a query based on the same criteria as the required Dynamic Distribution Group.