I am planning to upgrade my Exchange environment, 1 CAS, 1 HUB and 2 Mailbox servers in a DAG to upgrade to service pack 3. Currently they running without any service pack levels.
Once i upgraded CAS and HUB with Service pack 3, i am thinking to install a new Exchange 2010 SP3 mailbox server and join the existing DAG, add the Databases and move mailboxes to this new mailbox server. Then update service packs on other mailbox servers. Does this work? can i have at least for temporarily run DAG mailbox servers with different levels for service packs?