Email with no MX records

Hi

I have a few domains on CloudFlare which are intended for websites only. Accordingly they have A records and nothing else. The A records point to my rented server at online.net, which runs Debian Buster. I don’t believe that server should be able to receive SMTP mail; certainly I have not intentionally set it up to do so, although it is set up to send mail using sendmail.

Anyway, I am interested to know what happens if someone attempts to send an email to such a domain. My understanding of DNS is that absent an MX records, delivery should be attempted to any A records. However, with CloudFlare in place (proxying the DNS) that presumably shouldn’t be possible as the A records are blocked to the world. I would have expected the email sender to receive a bounce message from his mail server? In my case, I tested by sending to an arbitrary user @<domain.with.no.MX.records.com> using a gmail account, but I have had no bounce message.

Comment?

With thanks

If there is no MX record the email should bounce back. It could try the A record of the naked domain, but that - particularly in a proxied context - wouldnt work either. So only if your naked domain is not proxied it might try to deliver it directly to your server.

Yes, that’s what I thought.

Except, I read this:

https://superuser.com/questions/735226/how-is-email-able-to-reach-this-person-despite-no-mx-record

But as you say, with a proxy the sender’s email server should, at best, find CloudFlare. Just odd that the two tests I sent didn’t generate any kind of bounce message back to me.

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