Does mail dot com have IPV6 MX?

Just to be complete, this question remains unanswered:

Or, I did not find a way to get its ipv6 server?

Your methodology is correct but incomplete. The mail.com has two MX records:

$ dig mail.com. MX +short
10 mx00.mail.com.
10 mx01.mail.com.

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:

$ dig mx00.mail.com. AAAA +short
$ dig mx01.mail.com. AAAA +short

Because neither returns IPv6 addresses, the result does not change.

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.

gmail-smtp-in.l.google.com. 299 IN      AAAA    2607:f8b0:4001:c09::1b

For now, workarounds include run your own mail rely on a dual stack host, or run IPv6 transition mechanisms like NAT64.