A file that when created in the home
directory of your UNIX
shell account causes your mail to be forwarded to the address(es) in that file
Handy for vacations... create a file with your shell account's address and your web mail address and mail will be forwarded to your web mail and saved in your INBOX.
This of course assumes that you're server is using sendmail or another program that checks for the presence of ~/.forward.
Example .forward file: