I keep Outlook open at work all day.
After I have read a message, I decide if I have to act on it, if I should save it, or if I can delete it.
If I have to act on it, I keep it in my inbox until it is done.
If there is nothing to act upon but I think I should save it, I sent it to my "Read&SentMay2011" archive on the file share.
If it is not worth saving (i.e. not business related), I delete it.
I set the option to automatically delete items in the Deleted Items folder upon exiting Outlook.
Anything I send gets put in the "ReadAndSentMay2011" archive at the end of the week.
At the end of the month, I will create a "ReadAndSentJune2011" archive and close the May archive.
I use X1 to index and search my archived emails.
This keeps my inbox and deleted items folder clean and everything I acted upon in one monthly offline archived folder.
I usually end up with no more than 10 emails in my inbox at the end of the day.
I close Outlook at the end of each day so the deleted items folder empties automatically.