Cancel selected emails confirmation
I have had the experience of selecting numerous emails (in order to delete them) and then trying to click another and missing it such that all currently selected emails are unselected. This is a bit annoying (and happens to me regularly).
I want to suggest an "Unselect all selected" "Confirmation Request" pop-up prior to selected emails being all unselected.
Anthony Smitha commented
If it behaved like Gmail and simply selected the message that you click on when you are in the middle of the selection, that would be an improvement. If it did it's own thing and opened the single accidentally-opened message, but when you returned to the inbox or folder you found those same selected messages still selected, that would also be an improvement. If you are selecting multiple messages, the intention of the user is to continue selecting messages until the user chooses an action to do. I can't think of a single instance where anyone would intentionally select a set of messages and then desire to have that message selection cleared by opening a message.