SPF, DKIM, and DMARC are acronyms for email security protocols that verify emails came from the domain name they claim to be sent from. Spam is a huge problem for internet service providers (ISPs). It’s estimated that over half of all emails sent are spam. To try and cut down the sheer volume of spam messages, ISPs use SPF, DKIM, and DMARC to verify that an email message was sent from a legitimate domain and the message hasn’t been changed in transit.