Before your archive data can be imported make sure the Control Panel account related to the import is correctly set up. The following settings are necessary to continue:

Check the archive settings under Email Security > Email Archiving. Archiving needs to be enabled for the domain/s. No postboxes which are part of the import should be added as an exception here.

Check if all mailboxes which are part of the import are created within the Control Panel under Settings > Mailboxes.

All alias domains which are part of the import need to be created within the Control Panel under Settings > Domains.