Technical information like SPF, Dkim, Return route and mx information are car-created with the Postal server and you don’t have to fret yourself on generating them singly using a third party service. nano /opt/postal/config/postal.yml Just scroll down and Track down the option for DNS. Then switch all the sample hostnames https://it-support-services46383.blogdanica.com/26089366/top-guidelines-of-magento-2-install