3.1 Using the Mail Tool
3.1.4 Deleting mail messages

Deleting Mail
To keep the list of received mail messages to a minimum (and to save disk space), you should periodically delete mail messages. There are a number of delete options. Choosing to delete the mail messages does not remove the mail. Rather, the messages are stored until you close the mail window. This gives you an opportunity to decide not to delete the message. You can force the mail program to delete any mail messages which were previously selected for deletion by clicking on Mailbox and then Destroy Deleted Messages.

Undeleting Mail
While you continue to work with the mail program, you can view a list of the deleted mail messages and undelete one or more messages from the list. When a message is undeleted, it will reappear in the list of received mail messages.