your wish is my command, you can now mass-delete inbox & outbox messages!
(note this feature only works on dekstop, not on mobile because itty bitty screens)
there are now checkboxes next to your inbox / outbox messages (when viewing on desktop),
and a button the right that says 'delete selected', so you can delete the selected messages on that page.
there is also a 'check all' box at the top if you want to select all the messages on the page.
Also, there is a 'Delete ALL' button on the bottom right, which will clear out all your inbox or outbox messages.
Note - there is a 'confirmation' box that comes up just in case you accidentally hit the button. Once your messages are gone, they are gone for good! Wish it was so easy to delete some other things in my life! XD