- If an item requires my attention, I leave it in the inbox, flagging the ones I need to handle first
- If I need to retain an email for a long time, I move it to one of a dozen, topic-named folders
- If I might need an email in the short-term, I move it to a short-term "30-Day" folder
- If I don't need an email retained at all, I hit the delete key
To automatically clean up my short-term emails, I've set the retention policy for the "30-Day" folder (Right-click "30-Day" ... Properties ... Policy tab), changing the "Folder Policy" to "1 Month Delete (30 days)". The system takes care of the cleaning from there.