On Friday afternoon last week, Yahoo made a simple change to its DMARC policy from “report” to “reject”.

[yahoo.tumblr.com ]

DMARC, which stands for "Domain-based Message Authentication, Reporting & Conformance", is a technical specification created by a group of organizations that want to help reduce the potential for email-based abuse by solving a couple of long-standing operational, deployment, and reporting issues related to email authentication protocols.