Local folders backup to a usb drive outside of em client help

I want to backup email saved in local folders to folder called backup emails on a usb hard drive outside of emclient so I do not loose any saved emails for bakcup security, how do I do that? I know about general program backup feature.

The best way to do this is to use the built-in backup. Quicker and safer to both backup and restore than doing it manually, and can be done without closing eM Client. Specify a backup directory on your USB at Menu > Tools > Settings > General > Backup. 

If you want to do it manually, you can backup %appdata%\eM Client.
This is C:\Users\username\AppData\Roaming\eM Client on Windows 10. These are exactly the same files that the built-in back will copy. You need to make sure that eM Client is not running when you do this or some of the files may not copy, and could result in restore failure.