Syncing folders between Third Party Clients and Webmail prior to migration
In previous migrations that Atmail has performed they have noticed that some Third Party Clients (Outlook in particular) have removed local folders after the migration. The best way to ensure that this does not occur is to ensure that folders between Webmail and the Third Party Client are synced.
Instructions on how to do this for Outlook can be found here
If during this process you find that you need to subscribe to newly created folders via IMAP, instructions on how to do this for Outlook can be found here