Enhanced SPAM Protection for EOP

Exchange Online Protection (EOP) has recently been extended to provide improved SPAM protection.  The new functionality includes DMARC (Domain-based Messaging and Reporting Compliance) and DKIM (Domain Keys Identified Mail) for IPv4.  EOP has supported DKIM for IPv6 for a while.

DMARC uses the SPF framework to check the 5322.From address.  This is the address that appears in the e-mail client.  Traditional SPF only checks the 5321.MailFrom address.

DKIM allows a client to insert a digital signature into the header of a SMTP message.  This signature can then be verified against the Public key of the purported sending domain.

More details can be found at http://blogs.office.com/2015/01/20/enhanced-email-protection-dkim-dmarc-office-365/