Exchange/Outlook over a WAN connection

I’m considering migrating our domino/lotus notes to an exchange/outlook email solution. Currently we have one domino server located at our HQ location with 15 locations connecting to their mail database through various connections (Frame, DSL, Cable). It seems to work okay with Domino. I’m interested in learning if anyone has knowledge on how exchange/outlook works over a WAN connection. Budget does not allow us to put servers at each location, but we want users to be able to use the full outlook client. Any help would be appreciated.