If a wildcard character is present in the MX record, the GUID is NOT registered. The Event log contains:
Event Category: None
Event ID: 5774
Time: 3:38:21 PM
Description: Registration of the DNS record '0ae9d36d-1c8c-4aa4-8130-11a140138bc6._msdcs.Name.com.
600 IN CNAME <ComputerName>.Name.COM.' failed with the following error:
DNS RR set that ought not exist, does exist.</b>