To do it right, you'll have to add a switch to dmail to set \Deleted, that works much like the existing -s switch that sets \Seen.
However, I question why you want to do this. What's the point of delivering a message if it's going to be deleted?
-- Mark --
http://staff.washington.edu/mrc Science does not emerge from voting, party politics, or public debate. Si vis pacem, para bellum.