We have a 2003 domain with exchange 2003. We are migrating our exchange to exchange online. When I originally looked into this I found that I would need two servers one to host the ADsync piece and the other host federation services. I am wondering if this is still the case or now can I just put one 2008 standard r2 server in place to host ADsync and password sync? We will be upgrading the domain but not till 2015. We are going to migrate 20 mailboxes to exchange online using the staged migration because some users have mailboxes in excess of 5 GB. I know this takes an long time.... so I will have it syncing mail for a couple of months. Am I looking at the right solution or way off base?