There are several folders that should be cleaned out on a regular basis to avoid cluttered e-mails.

Click on a folder to view its contents.
To delete an e-mail, select it and click
. You can also delete many
e-mails at once. To do this, click on the first message that you want deleted and then hold down the
Shift key. While holding shift, click another e-mail. The two that you clicked
will be selected as well as all of the messages between them. Now click
.
The following folders should be considered when deleting message: Inbox, Outbox, Drafts, Sent Items, and Deleted Items, as well as any custom folders that you may have created.
When you delete an e-mail from a folder it will simply move the message to the Deleted Items folder. For this reason, be sure to clean out this folder last.