Archiving Exchange 2010 Mbx over a firewall

Hi there,

Im about to add an Exchange 2010 Mailbox server into our EV server but it sits on another site behind a firewall, can anyone advise me on what ports im going to need to open between to the two servers. It is within the same Domain.

I presume it wont need to talk to the CAS over there as its direct access to the Mbx?

Many Thanks