sendmail, 4th Edition

A Trick

In debugging large configuration files, the output that is produced by the -d21.15 switch can become too huge to examine conveniently. A good alternative (when modifying or adding rules) is to temporarily insert a fake subroutine call before and after individual rules to see what they do:

R$*      $:$>TEST $1       ← fake subroutine call
Rlhs     rhs               ← new rule
R$*      $:$>TEST $1       ← fake subroutine call

With the fake wrapper around the new rule (the name TEST is arbitrary), ordinary rule testing with -bt now shows how the address is rewritten by that rule:

3                  input: ...
TEST               input: ...
TEST             returns: ...
                                  ← new rule acted here
TEST               input: ...
TEST             returns: ...
3                returns: ...
>

If you use this technique, remember, of course, to remove the fake subroutine calls before putting that configuration file into use.