$ host prunille.vinc17.org Host prunille.vinc17.org not found: 3(NXDOMAIN)
As I said, this is a machine on a local network, not visible from the Internet. But the host can be resolved from the local network.
Many (most?) mailservers won't accept mail from a host who supplies a HELO hostname that doesn't exist in dns.
This is completely wrong. I've been using this since 2003-12-26, and this is the first time I get mail blocked for this reason. What is common is that mail is refused when the IP address doesn't have a reverse DNS, but my IP address has one.
You should fix your MTA
The MTA works as expected: it gives the FQDN, which is resolvable from the machines where the host is visible. The only machine that can see the local network and can be seen from the Internet is the NAT router, but it doesn't do SMTP forwarding.
(and/or have it smarthost out to a 'real' mailserver).
The smarthosts of my ISP often get blacklisted because this is a small ISP and this happens as soon as some client sends spam (probably due to a compromised machine). That's the main reason why I abandoned the smarthost solution. If someone knows how to configure postfix to select a smarthost for some domains only, this could be a solution (/etc/postfix/transport has some documentation, I'll have to try...). -- Vincent Lefèvre <vincent@vinc17.org> - Web: <http://www.vinc17.org/> 100% accessible validated (X)HTML - Blog: <http://www.vinc17.org/blog/> Work: CR INRIA - computer arithmetic / Arenaire project (LIP, ENS-Lyon)