We have an off-site AD domain (domain 2) connecting to the head quarter AD domain (HQ domain) through an AD trusted relationship so the domain 2's users can access the network resources in HQ domain. They are not in the same forest.
The Exchange server is located in HQ domain. Question to you, is it possible to create an Exchange mailbox at HQ domain using the domain 2's user account? Namely, do the Exchange users need to be the local domain users?