Looks like they change things every day (or hour?) > This is not Postfix.
Now, they announce thmeselves as Postfix:
220 VeriSign mail rejector (Postfix)
However, if you send a few
EHLO gizmo
RSET
it will answer sooner or later with a code 421 "too many errors",
which a real Postfix does not.
smtpscan was not able to reliably identify this server. It might be:
Postfix 1.1.11
Postfix 2.0.3
Postfix
Postfix 1.1.12
The fingerprint differs from these known signatures on 3 point(s)
