maybe this this is what you are looking for.
from start page hit your mail icon, select your mail account from messaging screen then select menu at bottom. from there select tools then options. at the bottom of the options page are 4 buttons select storage on this screen there is a box under (empty deleted items) select the arrow then select what you want to do, one choice is "immediately" mine is set on connect/disconnect. hope this is what you are wanting
IT