Change the routing status of a name suffix

To change the routing status of a name suffix

Open Active Directory Domains and Trusts.
In the console tree, right-click the domain node for the domain you want to administer, and then click Properties.
On the Trusts tab, under either Domains trusted by this domain (outgoing trusts) or Domains that trust this domain (incoming trusts), click the forest trust that you want to administer, and then click Properties.
On the Name Suffix Routing tab, under Name suffixes in the x.x forest, click the suffix for which you want to modify the routing status, and then click Edit.
In Existing name suffixes in x.x, click the suffix that you want to modify, and then click Enable or Disable.

Notes

To perform this procedure, you must be a member of the Domain Admins group (in the forest root domain) or the Enterprise Admins group in Active Directory, or you must have been delegated the appropriate authority. As a security best practice, consider using Run as to perform this procedure.
XOX
You cannot enable a name suffix that is in conflict. If the conflict is with a local UPN name suffix, then you need to remove the local UPN name suffix before you can enable the routing name. If the conflict is with a name claimed by another trust partner, then you will need to disable the name in the other trust before it can be enabled for this trust.
To view a log of name suffixes, DNS names, NetBIOS names and the status associated with this trust, click Save As. This log can assist you in troubleshooting authentication problems.
For information about trusts, see Related Topics.