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
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