mikeone, You are right and. Even this folder's path is hadly to find since it is sdcard/backup/AquaMail.
I vote for simplier path /sdcard/AquaMail or similar. Or, auto scan root of sdcard + Download folder for backup file. It's not so hard.
Paris Geek, you are right too, it works, but I don't consider it as the most user - friendly solution. When you need to change folders (to find one, where the backup file is) in Folder picker, why not choose the backup file directly in "Picker".