mail_data.dat is 16gb but nothing displays in eM Client

Hello, my mail_data.dat file is 16gb in size but in eM Client it shows nothing in any of the folders. Any idea why?

To test a few things out I also created a new storage location to reset eM Client to default settings and then I copied that 16gb mail_data.dat file over and started the application. No emails display in any of the folders as well.

I’m stumped. Is there any way recover what’s in that .dat file?