FYI: I had to disable ECN on our mail servers to be able to send mail to telecom.co.nz. So that's still an ongoing problem.
Their problem, not yours.
Unless you think that you should be conservative in what you send (see RFC3168).
I'm not sure what you mean by conservative but the reply I get when the
mail server sends a TCP sync with ECN is a Reset packet. Which is
documented as a big no-no. And is a know bug of Cisco PIX router for
example.
Anyway my point was just to let other people know so they don't have to
waste time trying to fix this.
jfp.
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Jean-Francois Pirus