I was prompted to upgrade this morning after launching EmClient and after doing so my entire mail database of several years and all my account settings (5 different mail accounts) have all vanished. I’m very unhappy already but if it turns out that I have lost my email I’m going to exceedingly unhappy!
If this can help, I am including here a post from Olivia (EM support):
sounds like you accidentally skipped the data migration from eM Client 6. This is needed because eM Client has a new database structure.
You can import these data manually using the Menu>File>Import>Import from eM Client 6 option.