by the way, the he support answer was
SMTP is not filtered to/from the system that performs the administrator
They may have misunderstood the question. But then again, I haven't seen the question you send to them.
I know the filters don't prevent going through the certification test, if you got the mailserver setup correctly. But the filter prevents anybody else from trying to connect to the server to find out, why it isn't working. That means you cannot just go to the forum and ask for help, because nobody on the forum can see what is happening behind the HE filters.
That is why I suggested that you go to firstname.lastname@example.org
and ask for the advice, you could previously have gotten from the forum. But they appear not to have understood that point.
I guess that just means whenever such question shows up, I'll advice people to setup a Teredo relay instead. No harm done, if many of the people going through the certification test learns to setup a Teredo relay. And now if you happen to want to ssh back home from your laptop, and you are somewhere with only IPv4 connectivity, then you can just use a Teredo client on your laptop. :-)