Problems with Exchange and RDP over a WAN link

[spies]

I have a site (Site A) with a pfsense box which currently has a SBS server below it.

This site now has a 100mbit leased line to another site (Site B), also with an SBS server.

The plan is to decommission the server at Site A, and use the active directory and exchange at Site B.

To start the transition, the DNS of the workstations has been changed to that of the SBS server at Site B. The machines have joined the domain and auto-discovered the outlook settings without issue, however, every 30 or so seconds they are losing connection with exchange and reconnecting, if an RDP session is open at the same time, this freezes for 20+ seconds and then resumes. The same thing occurs if I RDP to the SBS at Site B from the SBS at Site A.

This behaviour can also be observed when using OWA to the SBS server at Site B.

Site A uses a 10.233.* range and site B is using 192.168.0.*

The WAN of the pfsense at site A has 192.168.0.200.

If the workstations are connected to a switch above the pfsense box at Site A everything works perfectly, so the pfsense must be tarpitting or seeing something as an attack?

Has anyone got any suggestions?