I have an existing Exchange 2007 install. One server has three roles, CAS / HUB / and Mailbox. We are transitioning to Exchange 2010. I have installed the 2010 CAS / HUB roles on one server and the mailbox role on another. I have not moved any mailboxes as of yet. Everything still resides on the 2007 server. Internally, OWA works fine. If I go to https://internalmail/owa, I am prompted with the yellow 2010 OWA login screen (yellow screen = 2010, blue screen = 2007). I can login just fine and my mailbox appears with no issues. Externally, if I go to https://externalmail/owa, I am prompted with a new ssl certificate prompt and if I acceept, I get the yellow 2010 OWA login screen. So far so good. However, when I login to OWA, I get a page cannot be loaded error and the error mentions that the host is responding in a way that will never get resolved. I did change the address translations in the firewall. So, before the switch to 2010, the externalmail ip address 1.2.3.4 was pointing to 10.1.1.45, which was the 2007 all in one server. After installing 2010, I pointed the externalmail ip address 1.2.3.4 to 10.1.1.46, which is the new 2010 CAS / HUB server. Essentially, the external ip address on the public side did not change and still has the same dns name, externalmail. Only the internal ip address changed. So to end users, they still type in the same address that they have always used. Final note is that if I use a new external ip address for externalmail, for example 1.2.3.5 and map it to the new CAS / HUB ip of 10.1.1.46, OWA works externally just fine. What steps have I missed that allows the existing externalmail ip address of 1.2.3.4 for OWA to work externally? I can't seem to find the solution and I have searched extensively for the answer. Thank you in advance.

Thanks. I was able to get it going by setting up the legacy.comapny.com dns entries, both internal and external.

Thank you kindly for the detailed information. I found this article: http://blogs.technet.com/b/sjimmie/archive/2010/07/09/owa-coexistence-with-legacy-versions.aspx which explains how to configure the "Proxy" portion of the coexistence. Do you perhaps know if such configurations will work and is supported? If this solves the proxies for OWA, will this also work for Outlook Anywhere & other Remote Sync services such Blackberry Internet Services? Thanks in advance.