same problem here ... two emails stuck in the outbox (btw, no attachements, so they were just a few kb at most)
thanks @leojameselliot for the tip, cutting the machines internet connection indeed does bring up a delete option (!) seriously, what were the designers thinking.
(metro-)mail is nice at first glance but it lacks some serious features, even more for non-touch-users.
- collapsing/expanding imap folders - drag/drop support for moving/copying mail - deleting emails stuck in outbox folders (without the need to be offline to do so) - giving more info about what's going on (send/receive progress)