Backup and Restore -> missing Mails


I’ve changed my Notebook and wants to move my em-Client to the new Notebook.

Old one with 8.1.979 -> Backup
Move 5Gb zip to the new Notebook
New one with 8.1.1032 -> Restore

At first it looks fine for me.
But wait: I’missing a lot of mails in the Archive-Folder.

How can i fix that?