recover or open mail_data.dat.bak

hi i have a big problem …downloaded from imap mail into local folder almost 800 mb size emails  after i reopened EM Client, , local folder appear empty and i have a new file mail_data.dat.bak of 800 mb…any issue to try open that file or how reinstall it into EM client… i just read all forum… tried to rename .bak into .dat… any files…i’m very disappointed with this program…
pls help me i can pay for helps

It is best not to rename any files in the database directory, as that will break the database. As far as I know the bak file is only created after a database repair. You can try running the repair again and see if there is any difference. Close eM Client and run C:\Program Files (x86)\eM Client\ DbRepair.exe