What is "mail_data.dat-wal" file?!

I have an account with 15GB of DataBase and, in the same folder, there’s a file, that calls “mail_data.dat-wal” who has the same 15GB of size, so, the performance of my emClient looks like a pregnant turtle, what can I do with this file “-wal”??

Technically they are   W rite A head L og files. They are created when the first connection is made to the database file, and deleted after the last connection is made.  So if you close the database, you will see that the files are then removed. 

But, it’s normal the “-wal” file have the same size of the database?!

I just looked at mine, and it is about half the size of the .dat file, but it varies because previously I remember seeing it at about 30%.

You could close eM Client and run C:\Program Files (x86)\eM Client\ DbRepair.exe and see if there is any difference.

Okay Gary, thank’s for your attention, I will try this and then I return here with the results.

So can you use more that one mail_data.dat file seamlessly? Like using multiple outlook.pst files to keep the file sizes manageable. 

Yes, there is a separate mail_data.dat file for each email account, and a separate one for Local Folders, and also a separate one for search folders, and a separate one for the Archive.