Am 25.05.23 um 07:33 schrieb Slavko via mailop:
I am confused now as in RFC 7505 sect. 4.2 one can read:Null MX is primarily intended for domains that do not send or receive any mail... And: ...mail systems SHOULD NOT publish a null MX record for domains that they use in RFC5321.MailFrom or RFC5322.From addresses. I understand that RFC as: nullMX's primary purpose is about not receiving, but as side effect it can result as not sending too. Is my understanding wrong?
Technically, null MX and SPF "-all" are two different things, as has been pointed out. SPF "-all" is clear-cut, and you'd be absolutely correct in refusing to accept such mail.
However, null MX is a different beast. Technically it only states that a domain does not receive mail. But when you look at common use cases and exception situations such as NDNs, domains with null MX can be regarded as being not fully functional when used in RFC5321.MailFrom, as they will not receive and process technical feedback about deliverability. In my experince, this is a significant factor in assessing whether you want to receive mails from such domains.
RFC5322.From is a somewhat different matter, especially when null-MX domains are used in mails which are clearly not intended to be replied to. For bulk mail this is fairly common, although I would vastly prefer if such mails had a working RFC5322.From address for handling replies from confused recipients (a recipient who has not subscribed to some mailing list should be able to contact the sender and demand removal of his address without investing lots of sleuthing work to find out who was responsible for the e-mail). So this can be regarded as a sign that you would prefer to refuse such mail, but arguably a much weaker one, and one that more likely would cause false positives.
Cheers, Hans-Martin _______________________________________________ mailop mailing list mailop@mailop.org https://list.mailop.org/listinfo/mailop
