Surely the easiest way to backup my email is for MBL to do what it says on the tin:
It should be backing up my email, when it performs a category backup - like it says it will in the instructions, where it specifically says it will back up *.pst files. I would not expect to have to ‘faff around’ moving email around to ensure it gets backed up.
The idea behind all of this is to ensure I have a backup going on in the background at all times, which is particularly attractive to users, like my wife, who are NOT pc literate. That is the iniital attraction.