In Outlook on your device goto Menu->Tools->Options. Go to the message tab at the bottom and select "Keep copies of sent items in Sent folder."

This has worked for me, hopefully it'll work for ya'll

Also I have noticed (maybe I wasn't paying attention before?) that navigating in File Explorer is a whole heck of a lot easier as you can quickly hop back to the last directory you were in (when jumping from the storage card to main storage.) I just created a slew of shortcuts in record time!