OpenDMARC is an open source implementation of the DMARC (Domain-based Message Authentication, Reporting and Conformance) specification (RFC 7489), developed and maintained by The Trusted Domain Project, a 501(c)(3) non-profit.
OpenDMARC provides policy enforcement and aggregate report generation by combining the results of SPF and DKIM checks to make a pass/fail determination for incoming messages. Source code is available on GitHub.