Emails is being sent as .local

Hi Team,

 I have a test server running windows 2008 AD with domain.local configured. Then I installed Exchange 2010 on the same box, and was able to configure send an email to external email address.

The problem is if I sent an email using owa > the email is showing administrator@domain.local, hence I was not able to reply back on the email as it shows administrator@domain.local. But the administrator@domain.local was able to received email if I add a suffix as administrator@domain.com.

So the public dns registration is completed correctly, but I wonder how can I configure the AD or Exchange to  send and received an email as user@domain.com instead of user@domain.local.

Thanks