Messages are automatically deleted when they expire, but you can also delete them before the expiration date. 

To delete a message:

1.Select the InboxSent Mail, or Drafts tab that contains the message you want to delete.
2.Select the check box next to each email message you want to delete.
3.Select the Delete button.
4.Select the Trash tab and select the check box next to each email message you want to delete
5 select the Delete button. The message has now been permanently deleted and cannot be recovered.