The domain "%s" has been identified as an insecure domain for mail-enabled groups with hidden distribution list membership. ...

The domain "%s" has been identified as an insecure domain for mail-enabled groups with hidden distribution list membership. Hidden DL membership will be exposed to members of the built-in "Pre-Windows 2000 Compatible Access" security group. This group may have been populated during the promotion of the domain with the intent of allowing permissions to be compatible with pre-Windows 2000 servers and applications. To secure the domain, remove unnecessary members from this group.