sendmail, 4th Edition

Force Requeue on Error

Normally, a program in the user’s ~/.forward file is executed with the Bourne shell:

Mprog, P=/bin/sh,   F=lsDFMeuP,  S=10, R=20, A=sh -c $u
                                               ↑
                                         the Bourne shell

One drawback to using the Bourne shell to run programs is that it exits with a value of 1 when the program cannot be executed. When sendmail sees the exit value 1, it bounces the mail message.

There will be times when bouncing a mail message because the program could not execute is not desirable. For example, consider the following ~/.forward file:

"| /usr/local/lib/slocal -user george"

If the directory /usr/local/lib is unavailable (perhaps because a file server is down or because an automounter failed), the mail message should be queued rather than bounced. To arrange for requeuing of the message on failure, users should be encouraged to construct their ~/.forward files like this:

"| /usr/local/lib/slocal -user george || exit 75"

Here, the || tells the Bourne shell to perform what follows (the exit 75) if the preceding program could not be executed or if the program exited because of an error. The exit value 75 is special, in that it tells sendmail to queue the message for later delivery rather than to bounce it.