Moving some mailboxes before others

Whether you can move part of a domain to Zimbra and leave the rest on Exchange for now.

Yes. A staged migration lets both systems hold mailboxes on the same domain while you work through them, so you do not have to move everybody in one go.

This suits a large domain, or one where some people can be moved at a quiet time and others cannot. Mail continues to flow to both sides throughout.

Setting it up needs mail routing configured so that each address is delivered to whichever system currently holds it, which is work we do with you rather than something to configure alone. See Exchange to Zimbra migration for the wider picture, and speak to support before you start so the routing is in place first.