Problem with windows phone and owa

[nicksheppard]

Hey guys, we have a windows phone that connects to the mailserver just fine. Receives email and can send to any external mail address without problem. However phone cannot deliver any mail to local e-mail accounts, receiving a doesn't exist message. Tried delivering to .co.uk address they use and also .local (secondary e-mail suffix)

Connection is to an external public ip which port maps over to the exchange server. Users on the lan have no problems with their e-mail and remote access to owa works just fine.

Any suggestions.