DMARC stands for “Domain-based Message Authentication, Reporting & Conformance.” To determine the authenticity of an email message, DMARC protocol makes use of Sender Policy Framework (SPF) and DomainKeys identified mail (DKIM). DMARC requires both SPF and DKIM to fail in order for it to act on a message.
Your DMARC record is published alongside your DNS records including: SPF, A-recrds, CNAME & DKIM
Overcoming the limitations of SPF and DKIM, a properly configured DMARC policy can direct a receiving server to whether accept or reject an email from a particular sender. It is important to note that not necessarily all receiving servers will perform a DMARC check and act according to DMARC policy before accepting a message, but all the major Email Service Providers do and its implementation is being widely adopted.