Current production server is Exchange 2003 SP2 (v6.5 Build 7638.2) on Windows 2003 SP 2 Standard. New host has installed Windows 2008 R2 SP 1 with Exchange 2010 SP1 and custom installation of CAS. The plan is run a Transition Method from Exchange 2003 to Exchange 2010 moving mailboxes over time. OWA and OAB are currently in prodction using SSL (owa.contoso.com). I plan to use the same FQDN for the Exchange 2010 in support of OWA and OAB. I am not clear on the "New Exchange Certificate" option for "Legacy Exchange Server". I have purchased a new SSL for Exchange 2010 server. My plan was to use the same FQDN (owa.contoso.com).
My questions: Do I select "Use Legacy Domains" and can I use owa.contoso.com in the "Domain name to use for legacy servers"? Can I have OWA and OAB running on both Exchange 2003 and Exchange 2010 with same FQDN? What happens when I start migrating mailboxes?