| I run my own MTA for some 23+ years now. Google (supposedly) reads only my emails sent by their users and same can be said about other similar services. > The Simple Mail Transfer Protocol (SMTP) relies on MX records in the DNS to identify which server(s) it should hand the mail off to. Not necessarily (this statement is corrected later in the post). One of my domains have no MX records and I use it for email extensively. As per RFC2821, SMTP falls back to A (and AAAA which have not existed back then) when the FQDN does not have corresponding MX record [1]. I have only found it to be an issue with one web service which utilizes hunter.io, which marks my email address as invalid due to lack of an MX record. Real mail services work perfectly fine. They (hunter.io) have the following untruthful statement in their FAQ [2]: >> We check if there are MX records on the domain. If there aren't, the email address can't receive emails. Linked post reflects lack of requirement for the MX record correctly: > As it turns out, no explicit MX record is indeed the most widely found configuration: almost 119 million domains (58% of all domains) are lacking any such resource record. Of those, 76 million (64%) do have an IP address and thus could at least theoretically receive mail [1] https://www.rfc-editor.org/rfc/rfc2821#section-3.6 [2] https://hunter.io/email-verifier |
I think of it the other way around.
Originally, people would specifically say which computer it would be sent to when sending mail, right?
And then later came MX records.
So in my mind it’s like, ok send mail to this host, except if there are any MX records. If there are, then use those instead.