Re: [exim] DNS problems with sending via multiple smarthosts

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Author: David Purton
Date:  
To: exim-users
Subject: Re: [exim] DNS problems with sending via multiple smarthosts
On Tue, Jul 16, 2019 at 11:44:12AM -0700, Ian Zimmerman via Exim-users wrote:
> On 2019-07-16 15:03, David Purton wrote:
>
> >     2019-07-16 14:23:14 Start queue run: pid=12322 -qf
> >     2019-07-16 14:23:14 1hnFQ2-000379-9I no IP address found for host smtp.gmail.com
> >     2019-07-16 14:23:14 1hnFQ2-000379-9I == example@??? R=smarthost defer (-1): lookup failed for all hosts in smarthost router: host_find_failed=ignore host_all_ignored=defer
> >     2019-07-16 14:23:14 End queue run: pid=12322 -qf

> >
> > But I can look up the domain normally on my machine:
> >
> >     $ nslookup smtp.gmail.com
> >     Server:        8.8.8.8
> >     Address:    8.8.8.8#53

> >
> >     Non-authoritative answer:
> >     smtp.gmail.com    canonical name = gmail-smtp-msa.l.google.com.
> >     Name:    gmail-smtp-msa.l.google.com
> >     Address: 74.125.24.109
> >     Name:    gmail-smtp-msa.l.google.com
> >     Address: 2404:6800:4003:c02::6d

>
> nslookup does DNS protocol directly, while exim uses the system resolver
> library. This is some kind of a clue.


Maybe, but the host command has no problems, and I assume telnet uses
the system resolver and that has no problems either.

> Since the machine is a laptop with intermittent connectivity, how is
> /etc/resolv.conf managed? Does it always point to 8.8.8.8, or is there
> some hook in the scripts that bring wifi on/off line which can change
> the nameserver setting? If yes does that hook work reliably, and
> quickly enough for the resolver to pick up the change when exim flushes
> the queue?


Network connectivity is controlled by NetworkManager and that sets the
contents of /etc/resolv.conf. I can keep running exim -qf as long as I
want and the DNS look up never seems to succeed no matter how long I've
been on the network.

> And since the machine is a laptop, you probably run systemd right? Is
> systemd-resolvd active? (Although I can't imagine how exim might end up
> talking to it.)


I do run systemd. But systemd-resolved is not active:

    $ systemctl status systemd-resolved
    ● systemd-resolved.service - Network Name Resolution
       Loaded: loaded (/lib/systemd/system/systemd-resolved.service; disabled; vendor preset: enable
      Drop-In: /usr/lib/systemd/system/systemd-resolved.service.d
               └─resolvconf.conf
       Active: inactive (dead)
         Docs: man:systemd-resolved.service(8)
               https://www.freedesktop.org/wiki/Software/systemd/resolved
               https://www.freedesktop.org/wiki/Software/systemd/writing-network-configuration-manag
               https://www.freedesktop.org/wiki/Software/systemd/writing-resolver-clients



David

--
David Purton
e: dcpurton@???
m: 0413 626 862