I have two virtual CAS/HUBs and two physical MBX servers in a DAG. I made the MBX servers physicals back then because I didn't feel the supported configuration for MBX servers as virtuals was very concise. After reading this article I have decided to move the physical servers to virtual. I also have not deployed SP1. I was thinking I might build two virtuals to replace the physicals and deploy SP1 to the CAS/HUBs and the virtual MBX servers, but not the physicals. After deploying SP1 to only the physicals, can the mailboxes on the physicals be moved to the virtuals running SP1? Any issues there? My first go round with SP1 ended in disaster and I had to reinstall Exchange 2010 on the CAS/HUB back to RTM. ...Or should I just deploy SP1 to the physicals before moving mailboxes to the virtual MBX servers?