Ordinarily, sendmail
prohibits a user from running programs from inside a
~/.forward file unless that user also has a
valid login shell. This restriction is in place to prevent the
typical user from running any arbitrary program on a main mail
server. Some sites prefer to allow users to run arbitrary programs
despite the restriction about logging into the mail server. At such
sites, one can bypass this restriction by placing the following
special string in the /etc/shells file:
/SENDMAIL/ANY/SHELL/
If, for some reason, you need to use a different string, you can do
so by redefining WILDCARD_SHELL in
sendmail/conf.c.
If you enable arbitrary programs you should also implement the
sendmail restricted shell
smrsh. (See Section 5.8 for a
full description of smrsh.)
