I'm at the tests level for my company, but with ZCS 3 I had some problems while trying to use ImapSync to migrate.
It uses regular expressions and these where not correct, so, all mail where in odd directories like INBOX.Inbox ... I saw lines in the forum about this, but I didn't really understand what was the solution ...
)
If you have good results, I'm interested in your procedures.
If I have time to go forward this way, I'll inform everybody in this forum of my discoveries !