I had have recently look to disable SSL for Outlook Web Access to fit my need, in fact my Https port (443) was unfortunately already in used on my router.
Open the IIS 7 Manager.
Expand the Sites and click on Default Web site:
Click on SSL Setting icons from the list and disable the Require SSL.
and click on Actions: Apply.
Redirect the Http request to the OWA.
Install if this is not already installed the Http redirect from the Server’s Manager
Roles/Web Server (IIS) / click on Add Roles Services.
Select the Http Redirect.
Once installed. Open again the IIS 7 Manager, expand Site and click on Default Web site.
Click on the icon part of the IIS, Http redirect.
Add / Set Smart Host on Exchange 2007/2010
Open the Exchange Management Console.
Expand the Organization Configuration
Click on Hub Transport
Select the tabulation called : Send Connectors.
If and as your server is already running and operational, you should have had created
already an SMTP connector.
If so, right click and select Properties
Click the Network Tab. add the route mail through the following smart host option and add your internal SMTP Gateway that you wish email to pass through for external world