A program alias is a user ID that causes any mail sent to it to start a program that can accept the mail message for further processing. The alias consists of a path and executable file name, plus any required command line parameters.
When e-mail is sent to the program alias, the executable program is invoked and the entire contents of the e-mail message is passed to the executable program (as a .tmp file).
Tip: Be sure to delete the ".tmp" file after program execution to avoid excessive ".tmp" files building up in the spool file.