Well, I think I wrote here too early: from further investigation seems like the issue has gone and now those emails are not refused anymore.
According to the logs the issue lasted around 5 hours from 28/02/2024 07:00 CET to 28/02/2024 11:40 CET. I had no answer from their postmaster, so I don't know if they simply found the new rule was too aggressive or if it was a test and they will enable the rule in future. Stefano On Thu, 29 Feb 2024 at 10:00, Stefano Bagnara <mai...@bago.org> wrote: > Hi, > > we are an ESP (a very small italian alternative to Mailchimp). > > Today an italian mailvox provider started refusing our emails with this > message > > 550 5.1.0 <b+ourvariablereturnpath@e.#customerdomain> sender rejected: > domain does not have neither a valid MX or A record > > The "e.#customerdomain" is a CNAME record that points to app.mailvox.it > and app.mailvox.it has both A and MX records. > > I guess Tiscali is checking only the A and MX records for the sending > domain without following the CNAMEs: in many years this is the first time I > see something similar and I thought that many services sending email use a > CNAME like us as the alternative (zone delegation) is a lot more complex to > be setup. > > I just wrote email to Tiscali postmaster to understand if they will > consider this "a bug in the new feature" or a "feature of the new feature", > but in the mean time I wanted to share the issue as I think other senders > use the same CNAME solution. > > We use that CNAME host in order to align the SPF authentication of emails > sent by our customers but our email are also DKIM aligned, so I could > simply use @app.mailvox.it instead of the customer CNAME in the > return-path and emails would still pass DMARC via DKIM. > > Do you know other receivers refusing emails because the sender (smtp mail > from) domain is a CNAME? > > -- > Stefano Bagnara > Apache James/jDKIM/jSPF > VOXmail/Mosaico.io/VoidLabs > -- Stefano Bagnara Apache James/jDKIM/jSPF VOXmail/Mosaico.io/VoidLabs
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