When using caff from the signing-tools pacakge, it looks for sendmail
in the wrong places [1]. It would be useful to find a way to make it
work when installed.

I have found a workaround, which is to specify PERL_MAILERS as
sendmail:$(type -p sendmail), e.g.:

    PERL_MAILERS=sendmail:$(type -p sendmail) caff ...

1: /usr/lib/sendmail;/usr/sbin/sendmail;/usr/ucblib/sendmail