The xmailbox program displays, by default, an image of a mailbox.  When
there is no mail, the image shown is that of a mailbox with its flag down.
When new mail arrives, the image changes to that of a mailbox with the
flag up, its door open and a letter visible inside.  It can also optionally
play a sound through the sound-card. The NCD audio server, the rplay sound
package, FreeBSD Sun-compatible audio drivers, and an external sound player
program are supported.  By default, pressing any mouse button in the image
forces xmailbox to remember the current size of the mail file as being the
``empty'' size and to change its image accordingly.  In addition, the user
can optionally invoke his/her favorite mail retrieving program.