Hi, I'm planning how to upgrade my company's exchange 2007-environment to 2010. After reading a number of articles at technet and other forums, it seems that installing CAS and Hub-transport roles before installing av 2010-server with mailboxrole is recommended. On the other hand, it would be rather nice to install a mailbox-role first and move some mailboxes for test to be able to play with DAG and other features. Has any of you done this, or is it mandatory to install CAS and Hub-transport first?

Hi, I haven't tried to it the other way around, but all documentation from MS shows that you need the CAS/HUB before mailbox, this goes for installing service packs as well. There is no reason not to do it by the MS design since you don't ruin the setup you have by installing the new servers. So keep to the supported transition way and install CAS,HUB,UM and then Mailbox server. /MartinExchange is a passion not just a collaboration software.

It is not mandatory to install it first, but it is mandatory to have those roles installed. Exch 2010 MB server will not work without a 2010 CAS and HUB. All client connectivity needs the 2010 CAS and any email flow will need a 2010 HUB. Not sure how far you will get with just a 2010 MB in a 2007 Exch Org. Tim Harrington - Catapult Systems - http://HowDoUC.blogspot.com

It will not work. You can shut down CAS&HUB Exchange 2010 Server, and have only CAS&HUB Exchange 2007 servers alive, and it will not work, for mailbox located on Exchange 2010 Mailbox only server. There are differences in transport and the way CAS server communicate to Mailbox server. You can install CAS&HUB&Mailbox on the same server and deploy DAG. NLB for CAS will not work in this situation, but you can try DNS round Robin.