Robert Klemme sugested this for a user whose mail is delivered on a machine
where he is not allowed to log in and thus his shell is set to something
useless:
K> [Put] SHELL=/bin/sh [into .procmailrc.]
Stefan Monnier opined,
M> This should IMHO actually be either compiled into procmail or at least
M> put into /etc/procmailrc.
The default value of $SHELL compiled into procmail is overridden by the
recipient's login shell per /etc/passwd, so compiling it in won't help.
I believe that /bin/sh as a last-ditch default is already compiled in!
Putting it into /etc/procmailrc before the user's own .procmailrc (if it
exists) is read will work on systems where procmail is the integrated MDA.
If procmail is not the MDA but is called from .forward by the recipient,
nothing in /etc/procmailrc will do any good. (Then again, the only way
procmail can be called from .forward despite a dummy shell is for the dummy
shell to have some limited functionality, so I guess that the original
asker's site does have procmail as the MDA.)