Originally, I was trying to make "smtpd_sender_restrictions" work, but
Noel Jones (thanks again!) clued-me into the config-option
"authorized_submit_users" when using the sendmail (or derivative)
binaries. I tried unsuccessfully making some form of unix:group.byname
work like these options:
authorized_submit_users=!unix:group.byname, static:all
authorized_submit_users=!unix:group.byname=badUnixGroup, static:all
Short of creating a cronjob-script to regularly re/create a HASH file of
disallowed users in the Unix group, is there something obvious I am missing?