To the last post:
Here's the Mac link -> https://jacobsalmela.com/2013/10/30/ipv6-certification-walkthrough-enthusiast-level-hurricane-electric-part-3/

Sorry. It's my bad. I edited the first output to srv.mydomain.com. Both of them have only one domain and it's the same.

Per your text, different banners (host names) are being sent for IPv4 and IPv6.  Therefore, one of them doesn’t match the expected host name (manually entered or from the MX-RR).  Maybe that’s the problem.

Hello,
after a lot of issues (and fun, because there's no fun without issues  ) I finally have a working tunnel in my home network. The issues I had were mainly related to the Broadcom chipset issue that is preventing TCP sessions from correctly establish.

I live near Milan and I'm using the Zurich PoP, which is the one that is adding me less latency (about 20ms).

I was just wondering if you have plans on adding a PoP in Milan, since I see you already have three points of presence here

Thanks!

Hello,
this is a thing that made me struggling for many hours. Finally, I discovered this is a quite well-known Broadcom chipset issue:

https://ttlexpired.co.uk/2016/02/12/ipv6-tunnel-and-failing-tcp-sessions/

If you have full control of your router, you can issue those commands to disable flow cache:

fcctl disable
fcctl config --mcast 0

Maybe your router has some GUI options to toggle those settings, too.

Hi there,
I have the same problem with the Unexpected Banner, but when I telnet localhost I see this:
[darkness@srv ~]$ telnet -6 localhost 25
Trying ::1...
Connected to localhost.
Escape character is '^]'.
220 srv.mydomain.com ESMTP Postfix
quit
221 2.0.0 Bye
Connection closed by foreign host.
[darkness@srv ~]$
Then I do test to the IPv6:
[darkness@srv ~]$ telnet -6 2001:470:1f1b:ba:2001:470:1f1b:ba 25
Trying 2001:470:1f1b:ba:2001:470:1f1b:ba...
Connected to 2001:470:1f1b:ba:2001:470:1f1b:ba.
Escape character is '^]'.
220 srv.born2host.com ESMTP Postfix
quit
221 2.0.0 Bye
Connection closed by foreign host.
[darkness@srv ~]$
As I see from the previous comment it needs to be "220" and it is. At least HE to tell what banner they are expecting.

6RD is supposed to be run by your IPv4 provider, in place of 6to4 with their own address space. This isn't an IPv6 transition method we'd provide.

Hi is 6rd available in he net?
I need to experiment with a 6rd tunnel.
Thanks

Hi kcochran,

That would be a thing since mostly of my configs are IP's given by TunnelBroker.
I know that if I set up an DHCP server with a DNS server local, and point the NS records of the subdomain to the local DNS server would do the thing, but Im trying to figure it out if its possible through HE.net DNS servers, since this could be a little bit resource hungry if you are trying to run things from a router. Even though I have managed a way to run BIND on DD-WRT with the help of an external drive

That's not possible w/dns.he.net.  If you're using DHCP to assign addresses, you would need to run your own local name server and have DHCP send the updates to that one.