Firewall Appliance for a Small Business – Exchange Friendly

I need to replace our Firewall, our FVS318 by NetGear isn’t playing well with our hosted Exchange service. (Basically, I can’t create a rule or a ‘Trusted Domain’ to allow full port access to our provider’s bank of Exchange servers.)

I’m looking at the WatchGuard X55e and the SonicWall NSA 240. Anyone have any feedback on either of these devices, or perhaps a device I should review?

Thanks.