- https://www.united-domains.de/blog/dmarc-anforderungen-von-google-und-yahoo/
- https://en.wikipedia.org/wiki/Sender_Policy_Framework – SPF
- https://en.wikipedia.org/wiki/DomainKeys_Identified_Mail – DKIM
- https://en.wikipedia.org/wiki/DMARC – “Domain-based Message Authentication, Reporting and Conformance”
- https://de.wikipedia.org/wiki/DMARC