you want migrate your mail server or mail server and domain?
I migrated a server SBS last week (with the Enterprise version of Nethserver).
Please note that the mail there are no problems with outlook. The problem exists if you want to use contacts and shared calendars.
You have to use active sync but it works well only from the outlook of 2013.
In my case, where necessary, I have replaced the older outlook with thunderbird (which works great).
Otherwise you have to buy outlookdav