Comment 27 for bug 1519331

I am seeing this issue on Ubuntu 17.04.

/var/spool/postfix/etc/resolv.conf is pointing at 192.168.122.1, which is the IP of my libvirt bridge - this is a result of dnsmasq interfacing with resolvconf, so that the host system can resolve local hostnames of guests on the bridge.

It's fine that 192.168.122.1 is listed (aside from the part where I've killed the dnsmasq there for unrelated reasons), but this differs from the host resolv.conf, which points to 127.0.0.53 first. We should *always* be pointing to 127.0.0.53 (systemd-resolved) on Ubuntu 16.10 and later. The fact that we aren't means postfix is racing systemd-resolved at boot.

I think it should be a sufficient fix for this bug, on 16.10 and later, to have /lib/systemd/system/postfix.service declare After=systemd-resolved.service.