It seems mail dot com does not have an ipv6 smtp server. It is a little weird for such a famous email service provider. Or, I did not find a way to get its ipv6 server? I used the following command to check its ipv6 server:
dig mx01.mail.com AAAA
But the output does not show an ipv6 address. How can I get its possible ipv6 servers?
You will find many more "big" mail providers which do not have an MX record with IPv6 address. This is reality: more than 20 years after the introduction of IPv6, most of the communication in the public internet is still done with the IPv4 protocol. And I do not think that this is going to change anytime soon...
Open an issue with their support how they need to support IPv6. At this point they are 10 years behind adopting the modern internet protocol.
IPv6 capable MX records point to names with AAAA records, yes. Here is one for gmail.com, unfortunately Google is one of only a few even among the large mail providers.
For now, workarounds include run your own mail rely on a dual stack host, or run IPv6 transition mechanisms like NAT64.
Just to be complete, this question remains unanswered:
Your methodology is correct but incomplete. The
mail.com
has two MX records:If any of the mail exchanger MX records has an
AAAA
record and there's an SMTP server listening on port 25 of the address, that would be enough to make the domain IPv6 capable. Therefore, you must check both:Because neither returns IPv6 addresses, the result does not change.