sudo apt install opendkim opendkim-tools

sudo -u opendkim opendkim-genkey -D /etc/dkimkeys -d roamin-nomen.name -s Jan2026

create a TXT record for your domain using the selector and public key

Jan2026._domainkey

TXT

sudo cat /etc/dkimkeys/Jan2026.txt

( paste in from between the first quote to the last quote minus spaces )

e.g. dig +short Jan2026._domainkey.roamin-nomen.name TXT

sudo vi /etc/opendkim.conf

Syslog yes

SyslogSuccess yes

LogWhy yes

Canonicalization relaxed/simple

Mode sv

SubDomains no

OversignHeaders From

Domain roamin-nomen.name

Selector Jan2026

KeyFile /etc/dkimkeys/Jan2026.private

Socket local:/var/spool/postfix/opendkim/opendkim.sock

sudo usermod -G opendkim postfix

sudo opendkim-testkey -d roamin-nomen.name -s Jan2026 -vvv

Last line should say "opendkim-testkey: key OK"

sudo mkdir /var/spool/postfix/opendkim

cd /etc/postfix; sudo cp main.cf main.cf.before_dkim

sudo vi /etc/postfix/main.cf

milter_default_action = accept

milter_protocol = 6

smtpd_milters = local:opendkim/opendkim.sock

non_smtpd_milters = $smtpd_milters

sudo chown opendkim:postfix /var/spool/postfix/opendkim

sudo systemctl restart opendkim

sudo systemctl restart postfix