I am interested to migrate only a few users to the version of Zimbra NE, keeping my old server for other users.
I think that I must use the option of split-domain ( tell me if i am right, please) and use Zimbra as the primary, while for secondary server, my old one.

Now I've seen that with the trial NE version, i can migrate 50 users right? but if I have to keep my old mail server as I can create users that reside on the old saw that the guide says to create all users even on Zimbra?

My old server has 300 users, would I buy the licenses for the other 250 that do not migrate?

Thanks for the clarification
Good weekend