I just wasted 20 minutes of my life trying to empty out my "Sent" messages. I have courses in which a few hundred students receive a general email announcement or reminder from me, & I don't need to keep an individual copy of every single one of those emails. Right now, I can only delete 7 messages at a time, as that are all that fit on the screen. If I scroll down to select more messages, the ones at the top that are no longer shown get de-selected, for some reason.
Open for Voting