In this post i will capture the installation of opendmarc and how its configure alongside Opendkim.

Install opendmarc

apt-get install opendmarc

Configure systemd service file

cat > /lib/systemd/system/opendkim.service <
The specific changes here are lines #9 EnvironmentFile #13 -p $SOCKET
Defaults File
cat > /etc/default/opendmarc <
Opendmarc Config file
cat > /etc/opendmarc.conf <
Modify Postfix milters
 If you are running both opendkim and opendmarc your milters will look like this:
non_smtpd_milters = inet:127.0.0.1:12301, inet:127.0.0.1:12302
smtpd_milters = inet:127.0.0.1:12301, inet:127.0.0.1:12302
Restart the service
systemctl daemon-reload
systemctl restart opendmarc
systemctl restart postfix
DNS
Now go modify your DNS, adding a TXT record ‘_dmarc‘with the value ‘v=DMARC1; p=none; rua=mailto:postmaster@example.com‘
When you have validated dmarc is working properly you can change p=none to p=reject
How can you validate it?
There are a number of tools online to help you with this, also you open up a mail in google and click ‘show original’.

  
Enjoy
Other resources
 https://www.google.com/search?q=opendkim+setup
https://www.google.com/search?q=opendmarc+setup