There are two possibilities.  First, it will take until noon Wednesday, March 11 for us to move all mailboxes to the new server.  So if you are looking before then, your folders may not have been moved to the new server.

The other possibility is that you may need to subscribe to your old email folders after they have been migrated to the new server.  Some email programs will show all of your folders automatically (Eudora, Mac Mail), while others will only show the folders you have explicitly subscribed to (Thunderbird, Webmail).

Regardless of the email program you use, once your mailbox has been moved, you should see the old email that was in your Inbox.  If your old email is in your Inbox but you don't see other folders, use the instructions below to subscribe to your folders.

Thunderbird (Windows and MacOS)
Webmail (Windows and MacOS)