Joachim Fahrner <jf@???> wrote:

> I get lots of those errors in my postfix log:
>
> Jul 3 18:09:16 server postfix/smtpd[2840]: NOQUEUE: reject: RCPT from tupac2.dyne.org[178.62.188.7]: 450 4.7.1 <tupac2.dyne.org>: Helo command rejected: Host not found; from=<dng-bounces@???> to=<jf@???> proto=ESMTP helo=<tupac2.dyne.org>
>
> Is there some configuration problem with the list mail server?

As others have said, it's a DNS issue.

Specifically, your config has (IMO correctly) checks enabled on the HELO hostname. The list server is sending HELO=tupac2.dyne.org, and your server is trying to resolve that - the specific message means that DNS lookup is failing. It's resolving for me here (otherwise I wouldn't be getting list messages !) so you need to look at your local DNS setup.
What do you get if you ask "dig tupac2.dyne.org" or "host tupac2.dyne.org" ?