After upgrading to SOM 7.8 or with a new install of 7.8 the Internal and External Message Delivery Health Tests fail with a status of Not Complete. The details of the error are "Active Directory query failed"
Full Error Details
Active Directory query failed. DN=CN=DatabaseName,CN=Databases,CN=Exchange Administrative Group (FYDIBOHF23SPDLT),CN=Administrative Groups,CN=OrgName,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=DellSupport,DC=org, filter=objectClass=msExchMDBCopy, scope=OneLevel, attributes=cn.
Verify that the source mailbox is available and the test account has rights to access the mailbox in the Active Drectory..