Update eM Client -> Mail gone and can't use previous backup

We updated to the last version of eM client (7.2) and now all email is gone. I am not sure from which version the update was performed, I am looking into this for someone else. 

However, I have a backup which seems to contain the previous  “AppData/Local/Em Client” folder. It contains a mail_data.dat file which is 7 gigs big, so I am sure this contains the old emails but I just can’t seem to get it back into eM client.
I have tried to copy this backup folder over the AppData folder, but it eM-client just behaves as if it was newly installed. I have tried to use the import function on this folder but also without any luck.

Does anyone have any idea of how to get this folder back into eM-client? 

if you have a backup or look under c:\program files x86 and see if the database files are under the em-client folder

I assume the previous version as 6.x.  Go to menu/file/import and select “eM Client 6”.  The database format was changed in the 7.x versions and the update routine does not delete the old database.

Thank’s for the reply. I think that the previous version was 6.x but i’m not sure because I have tried using the import function but unfortunately I get the following message when I select the folder:

“This folder does not contain any em client data files or the data files were created with a version of em client that’s too old.”

Is there any way to find out which version was used?

I have this issue, was it ever resolved?