I managed to resolve this issue with some strange workaround.

I must confess, I dont exactly know which service was handling DNS before, as
NetworkManager and systemd-resolved were both disabled.

/etc/resolv.conf was overwritten by each DHCP request.

So I did the following.

I configured systemd-resolved to also listen on, and to use as DNS Server.

I then set the 6 domain-name-server DNS option on DNS for the host to
point to ( was not allowed).

So each DNS request is not sent to, which is the local
systemd-resolved. This then looks at the /etc/hosts file for matches, and 
queries to if no matches are found.

Now OpenSMTP connects to the internal IP, but can still use SSL/TLS and verify 

Strange strange...

When I have some more time I will switch OS to OpenBSD.

Thanks for your help!


> Hey yall, 
> in my smtpd.conf file I have "relay smtps://host.domain.tld"
> host.domain.tld does resolve to a public IP, and this needs to be a public IP 
> on
> public DNS.
> However, OpenSMTPd needs to relay to the local IP address of the smarthost.
> Since I have no DNS server running on that network, and i dont want to setup 
> a DNS
> server only for OpenSMTPd, I added an enty to /etc/hosts, assigning the local 
> IP to
> the FQDN.
> When i ping the FQDN it correctly resolves to the internal IP of the 
> smarthost.
> However, OpenSMTPd ignores the entry in /etc/hosts and still tries to connect 
> to the
> public IP of the host.
> Is this known that OpenSMTPd ingores /etc/hosts? Or is this a problem on 
> Debian?
> Is there a workaround? Specifying "relay smtps://" will not 
> work, as the
> private IP is not part of the Cert. 
> Can I force OpenSMTPd to use the internal IP? Can I disable Cert checking for 
> the
> smarthost?
> Thanks!
> System details:
> root@mx01:~# lsb_release -a
> No LSB modules are available.
> Distributor ID: Debian
> Description:    Debian GNU/Linux 11 (bullseye)
> Release:        11
> Codename:       bullseye
> root@mx01:~# smtpd -h
> version: OpenSMTPD 6.8.0p2
> usage: smtpd [-dFhnv] [-D macro=value] [-f file] [-P system] [-T trace]
> root@mx01:~# cat /etc/network/interfaces
> # This file describes the network interfaces available on your system
> # and how to activate them. For more information, see interfaces(5).
> source /etc/network/interfaces.d/*
> # The loopback network interface
> auto lo
> iface lo inet loopback
> # The primary network interface
> allow-hotplug ens192
> iface ens192 inet dhcp
> Any info else you need?
> Cheers, 
> Simon

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