The messages could be phishing attempts, or ploys intended to trick recipients into revealing sensitive information or encouraging them to click on malicious links leading to bogus websites purporting to be, for example, a bank.

"If you receive an email claiming that it is from your bank, the applicable DMARC policies require the email to prove that is indeed from your bank in order to be delivered to your mailbox," wrote Ajay Gopalkrishna , a senior product manager with Yahoo Mail. "If the incoming email cannot be verified, Yahoo Mail will not deliver the email to your mailbox."

Gopalkrishna wrote Yahoo will encourage ISPs and other email providers to deploy DMARC. Organizations and companies behind DMARC intend to submit a draft specification to the Internet Engineering Task Force in the hope it will become a standard.