Sources:
https://serverspace.io/fr/support/help/postfix-as-a-send-only-smtp-on-ubuntu/
https://postfix.traduc.org/
https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-postfix-on-ubuntu-20-04-fr
https://www.malekal.com/installer-configurer-postfix-spf-dkim-dmarc/
https://lea-linux.org/documentations/DKIM_SPF_Postfix
