I noticed I could no longer send email recently. This is the behaviour
when I try to run sendmail from and older opensmtpd (this output
suggests it works):

→ /gnu/store/6843f93hfr54ds5zzl7ik3h5njgicy0w-opensmtpd-6.6.4p1/sbin/sendmail -h
sendmail: illegal option -- h
usage: sendmail [-tv] [-f from] [-F name] to ...


However with a more recent version, it doesn't work:

→ /gnu/store/j1mf5gdzf9i1r6sv4nl0yisk2nswzdfz-opensmtpd-6.7.1p1/sbin/sendmail -h
sendmail: this program must be setgid smtpq


Any ideas?