External Trust RDP server issue

Hi 

I have External Trust between other domain (corp.contoso.com) with my domain (my.domain.com).

Corp.contoso.com domains's user can access to resource of my domain resources.

But When Corp.contoso.com users trying to take RDP of my.domain.com server's, they are getting access denied.


How can they access the RDP of "my.domain.com" server from corp.contoso.com eventhought I have open port from my DC to corp.contoso.com DCs.