Trying to access OWA via http://servername/ forwards to https://webmail.domain.com/owa… Where is this configured

You're doing it backwards - is there a reason for this?

This is the way it's supposed to work.

• Before you install Exchange 2010, you have Exchange 2003 on https://mail.acme-widgets.com
• You create legacy.acme-widgets.com and make sure your firewall forwards traffic destined for this to Exchange 2003
• You change DNS records/firewall rules so traffic destined for https://mail.amce-widgets.com is now forwarded to Exchange 2010.

When you do this, any users whose mailboxes are on Exchange 2010 will use the Exchange 2010 OWA that they have logged in to (using the external or internal URL), and any mailboxes on Exchange 2003 are forwarded to an Exchange 2003 server that you specify.

To set the URL your Exchange 2003 users are sent to, run this cmdlet Set-OwaVirtualDirectory <Your OWA Virtual Directory> -Exchange2003Url https://legacy.acme-widgets.com/exchange.

Since there are no answers for this I thought I would provide you with a hack that could fix this.

On your OWA front end servers set your 404 page to redirect back to the login screen.

Here is an article on how to do this in II7.

http://technet.microsoft.com/en-us/library/cc771076%28WS.10%29.aspx

Hopefully this will tide things over until you can completely remove 2003 from your organization. Obviously redirecting any 404 to the login page is not ideal.