The specification, called (Domain-based Message Authentication, Reporting & Conformance), allows email senders to tell receiving services if they are using two other technologies to weed out spam.

Many email senders use DKIM, or DomainKeys Identified Mail, which wraps a cryptographic signature around an email that verifies the domain name through which the message was sent.

The second technology, SPF, or Sender Policy Framework, allows email senders to indicate which hosts are authorized to send their email, allowing receiving organizations to discard messages coming from spoofed "from" addresses.

The DMARC specification, which is supported by companies including Google, Facebook, Microsoft and others, lets a sender indicate if they are using SPF or DKIM, or both. It also allows senders to tell the recipient what to do with messages if authentication of some messages fails.

Senders can also receive a report from recipients on how they've handled the questionable messages. DMARC helps solve the problem of what to do with suspicious messages, which in some cases might have been delivered.