Dkimsign

$ doas groupadd -v _dkimsign
$ doas useradd -s /sbin/nologin -d /var/empty -g _dkimsign -G _mail _dkimsign
$ openssl genrsa -out private.key 1024
$ openssl rsa -in private.key -pubout -out public.key
$ chmod og-rwx private.key
$ chmod og-wx public.key
$ chmod u-w public.key private.key
$ doas mkdir /etc/mail/dkim
$ doas mv private.key public.key /etc/mail/dkim/
$ doas chown -R _dkimsign:_dkimsign /etc/mail/dkim/