Allegedly, on or about 26 January 2016, arnaud gaboury sent:
Now when testing with telent, I don't have the answer expected : 220 mail.thetradinghall.com ESMTP Postfix
$ telnet mail.thetradinghall.com 25 Trying 212.147.52.214... Connected to mail.thetradinghall.com. Escape character is '^]'.
That's the kind of response I get if I telnet to my mail server, other than the Escape... and Connected to... lines are in the opposite order.
Just by the by, further up in your message you did:
$ dig mail.thetradinghall.com @ns1.he.net
You'd want to check that you get the same results when not asking a particular name server, to see what the default name server tells you. Because that's (the default name server) what's going to get used with other commands and programs.