The domain controller could have the Exchange schema without actually having Exchange in the domain.
In order for the AD Connector to be able to update the Exchange schema attributes the connector needs to detect that there is an Exchange in the domain. The connector will end send a subtree ldap search against the domain controller with a BaseDN of "CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=***,DC=yyy,DC=zzz" and a filter of "(objectClass=msExchAdminGroupContainer)" and the connector needs to find a result. The ID used to acquire the connector also needs to have certain permissions as mentioned in the product doc link:
Privileges Required to Connect to the Exchange Endpoint - CA Identity Management & Governance Connectors - CA Technologi…
Assuming the ID has the proper permissions and there is an Exchange in the Domain and that ID can find an object in the above mentioned search then you can run the command mentioned in the below KB to cause the AD Connector to retry the above mentioned search and refresh the endpoint to detect Exchange:
How to register a New or additional Exchange Serve - CA Knowledge