Problem: Send As permissions are not setting in the panel
If the Owner of the AD object is different from the user configured in Exchange Server role in HC at Configurations >> Servers >> Edit Exchange Server. Normally this case appears if you have created the user manually in the Active Directory and later you enable mail services.
To see the owner of the AD object, open Active Directory by clicking Start >> run >> dsa.msc and then navigate to Organizational Unit > Select Account >> Properties >> Security >> Advanced. For further clarity see the screen below:
Resolution : To resolve the issue, you must modify the owner to reflect the same user that is configured in HC Exchange Role Configurations.