An area in
memory or on a
storage device where
e-mail is placed. In e-mail
systems, each
user has a private mailbox. When the user receives e-mail, the mail system automatically puts it in the mailbox.
The mail system allows you to scan mail that is in your mailbox, copy it to a file, delete it, print it, or forward it to another user. If you want to save mail, it is a good idea to copy it to a file, because files tend to be more stable than mailboxes.
Also see Why E-Mails Bounce in the Did You Know section of Webopedia.