I have done a lot of thinking about the current confrontation and how to bridge it.
The problem seems rooted in our different attitudes toward the PSL. If one assumes that the Tree Walk must displace the PSL completely and quickly, then it becomes necessary to “make do” with incomplete information about organizational boundaries, even though this introduces unwanted risk to evaluators. I believe that the assumption is unnecessary, because the Tree Walk and the PSL can coexist without harm. We simply specify that the Tree Walk algorithm MUST be used when organizational boundary information is known to be complete and certain, as indicated by specific policy tags, while the PSL MAY be used when boundary information is uncertain or incomplete. The “Must-use-Tree-Walk” indicator provides the domain owner with a remedy to correct PSL errors, as well as a strategy for avoiding them. The MUST indicator also means that DMARCbis-compliant implementations MUST implement the Tree Walk algorithm, ensuring that the new algorithm becomes deployed with critical mass. The “MUST-use-Tree-Walk” assertion is accomplished with a DMARC policy tag on the organizational domain record, supplemented by DMARC policy tags to indicate the boundaries of any contained sub-organizations. Some processing guidelines will need to be provided to ensure that the Must-use-Tree-Walk indicator is always found when it is present. Doug
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