$ 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/