Re: [dmarc-ietf] Using CNAME records to DMARC templates causes issues
jbouwh <dmarc-list@jbsoft.nl> Tue, 02 March 2021 12:09 UTC
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Date: Tue, 02 Mar 2021 13:09:25 +0100
From: jbouwh <dmarc-list@jbsoft.nl>
To: Douglas Foster <dougfoster.emailstandards@gmail.com>
Cc: Tim Wicinski <tjw.ietf@gmail.com>, Henning Krause <mail=40henningkrause.eu@dmarc.ietf.org>, dmarc@ietf.org
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Subject: Re: [dmarc-ietf] Using CNAME records to DMARC templates causes issues
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L.S. I would suggest update the DMARC standard make explicit how CNAME can be used or not. Beside of that, the opendmarc software should address this as a bug in some way. Their opendmarc-check tool shows the correct policy that fails from the opendmarc service when used on a CNAME-ed DMARC policy. The usecase I have seen failing only was one CNAME level deep. The failing mechanism in opendmarc for fetching the DMARC policy now seems to leed leads to a 'none' policy. Regards, Jan Douglas Foster schreef op 2021-03-02 12:51: > 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 <tjw.ietf@gmail.com> > 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 >> dmarc@ietf.org >> https://www.ietf.org/mailman/listinfo/dmarc > _______________________________________________ > dmarc mailing list > dmarc@ietf.org > https://www.ietf.org/mailman/listinfo/dmarc
- [dmarc-ietf] Using CNAME records to DMARC templat… jbouwh
- Re: [dmarc-ietf] Using CNAME records to DMARC tem… Tõnu Tammer
- Re: [dmarc-ietf] Using CNAME records to DMARC tem… Henning Krause
- Re: [dmarc-ietf] Using CNAME records to DMARC tem… Tim Wicinski
- Re: [dmarc-ietf] Using CNAME records to DMARC tem… Douglas Foster
- Re: [dmarc-ietf] Using CNAME records to DMARC tem… jbouwh
- Re: [dmarc-ietf] Using CNAME records to DMARC tem… Tõnu Tammer
- Re: [dmarc-ietf] Using CNAME records to DMARC tem… Seth Blank
- Re: [dmarc-ietf] Using CNAME records to DMARC tem… Murray S. Kucherawy
- Re: [dmarc-ietf] Using CNAME records to DMARC tem… Tim Wicinski
- Re: [dmarc-ietf] Using CNAME records to DMARC tem… John Levine