Every time you delete an e-mail message, it goes into the Deleted Items folder. This folder can grow quickly, so you need to keep cleaning it out.
Since you probably intended to get rid of deleted items in the first place, permanently tossing them out is a painless way to cut the bulk.
You can specify when and how you want your Deleted Items folder tidied up: You can tidy up automatically every time you quit Outlook, or do it manually whenever you like.
Tidy automatically Select a check box, as shown in Figure 1, and your mailbox will be trimmer in no time.
Tidy manually If you prefer to have more control over when items are dumped from Deleted Items, you can empty the Deleted Items folder manually with a simple right-click, as in Figure 2, or you can use the Mailbox Cleanup dialog box. Are you noticing a pattern for this Mailbox Cleanup tool? It's a great resource for cleaning things up.