Sources :
  * https://www.linuxbabe.com/mail-server/spf-dkim-postfix-debian-server
  * https://www.mail-tester.com/
  * https://admin.alwaysdata.com
  * https://dmarcadvisor.com/fr/dkim-check/
  * https://check.spamhaus.org/

A venir, si la motivation est là