I know we can upgrade Exchange 2003 to 2010 directly in general, but not sure if it is still OK in my case.
My Windows 2003 AD domain controller and Exchange 2003 are in the same machine (called dc-exch). In theory, there are two options.
Option#1: Direct Exchange upgrade.
Step#1.1 Install Exchange 2010 on Windows 2008 (exch2010).
Step#1.2 Migrate all email functions from dc-exch to exch2010.
Step#1.3 Remove Exchange 2003 from dc-exch machine and turn it into a pure DC.
Option#2: First separate Exchange 2003 from DC, then upgrade.
Step#2.1: Install Exchange 2003 on Windows 2003 (exch2003).
Step#2.2: Migrate all email function from dc-exch to exch2003.
Step#2.3: Remove Exchange 2003 from dc-exch and turn it into pure DC.
Step#2.4 Install Exchange 2010 on Windows 2008 (exch2010).
Step#2.5 Migrate all email functions from exch2003 to exch2010.
Step#2.6 Retire Exchange 2003 server (exch2003).
Q#1. Is option#1 feasible?
Q#2. If yes, any precautions during the transition?