Because CNAME usage was not mentioned in the previous DMARC document, existing implementations may not have tested this configuration. For the policy publishing organization, this increases the possibility that some recipients may treat the mail as not protected by DMARC. As with any deployment issue, the publishing organization has no reliable way to know if the deployment of DMARC implementations with full CNAME support is "essentially complete". This uncertainty may be acceptable for some organizations, but may be an obstacle for others, depending on their motivations for implementing DMARC.
On the implementation side, the use of CNAME will introduce the possibility of referral errors, which may or may not require mentioning in the DMARC specification, since such issues have probably been addressed in core DNS documents. The issues that come to mind are: CNAME referrals to non-existent names Nested CNAME referrals (what depth is allowed?) CNAME referrals that produce loops or excessive nesting depth. DF On Tue, Mar 2, 2021 at 6:12 AM Tim Wicinski <[email protected]> wrote: > > Using a CNAME at _dmarc.example should not be a problem, as long as > the CNAME target is a TXT record. The DNS resolver functions should > should handle this seamlessly. This does sound like a vendor software > problem. > > I am aware of DKIM records being deployed using CNAMEs pointing to a TXT > record target. > Has anyone seen the above error condition when testing DKIM records? > > This definitely sounds like an issue with the software. > > Nobody should shy away from publishing DMARC records that are CNAMEs to > DMARC > TXT records elsewhere. Using this design should be strongly encouraged. > > tim > _______________________________________________ > dmarc mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/dmarc >
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