I have OWA working perfectly internally and externally via port 443. I also have RPC over HTTP working within the office. I setup an A Record with my domain registrar with mail.domain.com i also setup a CNAME within DNS so mail.domain.com can resolve to the exhange servers internal IP.
I also have port 6001-6004 open. Not sure wether i need to have a trusted ssl certificate for this work out of the office. If anyone can help me out i would much appreciate it.