The design of DMARC precludes grouping policies for a set of domains above the organizational level, such as TLDs (Top Level Domains). These types of domains (which are not all at the top level of the DNS tree) can be collectively referred to as Public Suffix Domains (PSDs). For the subset of PSDs that require DMARC usage, PSD DAMRC provides an extension to DMARC to enable DMARC functionality for such domains.
Not all PSDs are suitable for PSD DMARC. Details are described in the internet-draft linked below. In order for receivers to know if the query for a PSD DMARC record should be made, some kind of list or service (TBD) is needed in order to prevent inappropriate usage of PSD DMARC.
This web site is about DMARC (Domain-based Message Authentication, Reporting, and Conformance) Extension For PSDs (Public Suffix Domains) AKA PSD DMARC, a DMARC extension. DMARC (Domain-based Message Authentication, Reporting, and Conformance) is a scalable mechanism by which a mail-originating organization can express domain-level policies and preferences for message validation, disposition, and reporting, that a mail-receiving organization can use to improve mail handling. DMARC policies can be applied at the individual domain level or for a set of domains at the organizational level.
Example registry, query, and PSL extention services
In order to facilitate PSD DMARC development, psddmarc.org has created sample services to support DMARC engineering and testing. It is not meant for any kind of production use. This is intended to provide an engineering resource to assist in development of IETF DMARC working group consensus on the best path forward.
There is both an online registry provided largely in the style of ani IANA parameter registry (completely unaffiliated with IANA, just an example) and an online DNS based query service.
Additionally, there is a Public Suffix List (PSL) format extension provided by Alessandro Vesely.
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The online registry provides a csv file that is suitable (for testing only) to be downloaded and parsed ocassionally. The registry is not expected to change with any frequency.
The DNS query service is meant to provide ~real time responses on the PSD DMARC status of a particular public suffix.
The PSL extension uses the same format as the PSL. It is meant to be periodically updated using the same mechanisms as are used for PSL updates.