@Christophe; you're very welcome!
Pre-upgrade, all of your configurations will be of XML type, and will be found here:
C:\Program Files (x86)\SmarterTools\SmarterMail\Service\
Post-upgrade, these XML files are converted to JSON format and are stored in the Settings directory within the Settings directory. So, to revert any conversions implemented by the previous upgrade process you'll want to check for the presence of JSON files within:
C:\Program Files (x86)\SmarterTools\SmarterMail\Service\Settings
Deleting those JSON files should make your installation appear to be a pre-upgrade environment, and this will cause SmarterMail to reconvert the XML files into JSON during the upgrade process. Overall I'm sorry to hear you're having so much trouble with this upgrade process, and I can definitely understand concern in attempting it again. Your best line of defense on this is to get a full backup of the installation and domain storage locations before getting started. This will provide you a fall-back point should anything go wrong, as you'll be able to restore the entirety of the environment. Backup/Restore procedures are outlined here:
If you'd prefer to have our team carry out the upgrade for you - we do offer these services - and would be happy to help get this going in the right direction. Below you will find more details about those ticket types:
I hope that helps smooth out this process a bit for you. Have a great day!
Technical Support Specialist