Exchange 2010 Branch Office Setup

I am currently planning on setting up a branch office for a client.

Head office has a domain controller and a exchange 2010 server.

The two offices are already linked with site to site VPN.

I am planning on installing a server at the branch office for the purpose of a domain controller and exchange server.

Exchange will be setup with DAG to replicate between the two exchange servers

Brach office will have its own mail store database

My question is what roles are required on the branch office exchange server to have the branch office users connect to their mailbox directly on their server

Thanks