Links utili
- http://it.wikipedia.org/wiki/Sender_Policy_Framework
- http://robrota.com/dimmi-che-smtp-usi-e-ti-diro-chi-sei/
- http://social.technet.microsoft.com/Forums/exchange/it-IT/44414d00-b6d5-4bb5-a427-2d59dfc345eb/invio-mail-ko-spf-failed-not-authorized