If a wildcard character is present in the MX record, the GUID is NOT registered. The Event log contains:
Event Type: Error Event Source: NETLOGON Event Category: None Event ID: 5774 Date: 6/24/2002 Time: 3:38:21 PM User: N/A Computer: <ComputerName> 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.To resolve this problem, create the GUID manually. If DNS zone scavenging is enabled, select the advanced properties of the GUID record, and clear the Delete this record when it becomes stale check box.