Linking old server mailboxes to new server (without migrating data)?

[DynamicOwl]

My organization will be upgrading from Zimbra 8.5 to 10 and originally we were planning to migrate all data from the old server to the new one using rsync. However the amount of data that users have makes this approach quite arduous. We're now considering starting from scratch with the new server. We anticipate most users will still want to access their old mail. Is it possible to link users' old mailboxes to the mailboxes on the new server without any migration?

Thanks!