On Mon, Sep 16, 2019 at 01:44:38PM +0200, Helmut Schneider wrote: > Sep 16 06:08:09 h2786452 postfix-in/smtp[12937]: 194853E04AA: to=<info@>, > relay=none, delay=0.01, delays=0.01/0/0.01/0, dsn=5.4.4, status=bounced > (Host or domain name not found. Name service error for name=exchange01 > type=AAAA: Host not found)
You should explain how the name "exchange01" becomes the nexthop destination for mail to "<info@>" (which does not look like a valid email address). > I already created an entry in the hosts file without success. By default, the Postfix smtp(8) delivery agent does not consult /etc/hosts: http://www.postfix.org/postconf.5.html#smtp_host_lookup > Where can I change the DSN to 4xx and ensure that mails are delivered when > the tunnel is up again? Normally, if a tunnel goes down, DNS lookups that require access to a server on the far side of the tunnel tempfail, and Postfix would automatically return 4XX. If your system returns hard errors when the network is partly down, then that's a configuration defect with the system. -- Viktor.