When doing a migration from on-premises MS Exchange Server to Zoho Mail, is the new Zoho mailbox kept in continuous sync with the Exchange mailbox? I.e. can I start the migration before the actual cut over to Zoho Mail, and then, once the contents of the existing mailbox are all copied over to Zoho, perform the cut over (change the MX records, instruct the users to use Zoho instead of Exchange, etc)?

Or, are the contents of the old mailbox assumed to be static and unchanging, and the migration is a one-time copy, and therefore must be performed after the cut over?