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:
presto@shellacctdomain.xyz
presto@webmaildomain.xyz