I cannot get mailcow to work

Hello,

I have followed this tutorial to install mailcow: https://www.the-digital-life.com/mail-server-on-linux/

Now, when I visit: mail.mydomain.com, I see the same content as mydomain.com. I think there is something wrong with the DNS. See this: https://ibb.co/4YYf1yD

Mxtoolbox.com gives this error: Mail server failed to connect to SMTP server, and there is a problem getting the IP Address for the site.

Can you please advise on how can I get this work?

Thanks

One more point is that the IPV6 is as follows: 2axx:xxx:xxx:4b82::/64.

When I added this to the AAAA in the DNS record, I removed the / and made it like this: 4b82::64. I am not sure if there is anything I miss here.

root@mail:~# host IP-address

Host IP-address not found: 2(SERVFAIL)

root@mail:~# nslookup NS1.domain-name.com

Server: 127.0.0.53

Address: 127.0.0.53#53

** server can't find NS1.domain-name.com: NXDOMAIN

How to fix this?