You don't need to open messages in order to delete them. If you want to delete multiple messages at once, select those messages, and press Del. If you want check boxes, use web mail.

That's a bit of a hassle though. Most mail services have a trash button for every message so you can delete them as you go along. Maybe if there was a way to enlarge the 'Deleted' folder icon/text on the left pane so I could drag the messages there easily?

My way is using the up and down keys to move and select (sometimes with caps-key) then del-key to delete. It's often to fast.

Okay thanks