Re: Configuring Exim for mail delivery

From	Mark Fletcher <mark27q1@gmail.com>
Newsgroups	linux.debian.user
Subject	Re: Configuring Exim for mail delivery
Date	2016-10-01 15:40 +0200
Message-ID	<snsGe-D4-13@gated-at.bofh.it> (permalink)
References	<sncBs-6LW-5@gated-at.bofh.it> <snhKO-1ya-1@gated-at.bofh.it> <snpS2-7al-23@gated-at.bofh.it> <snrAu-8pp-7@gated-at.bofh.it> <sns3v-97-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Sat, Oct 01, 2016 at 01:56:40PM +0100, Brian wrote:

> The thing for Mo to grasp is that exim *always* does an MX lookup, often
> using the ISP's DNS server. user@server will fail (as has been found
> out) because the domain "server" is not in the DNS.
> 
> /etc/hosts is not consulted when the lookup is done. exim can be made to
> look at /etc/hosts but for such a simple setup it is not worth the
> effort and would likely lead to a world of pain.
> 

With great respect I think that confuses the issue. A DNS lookup will 
*not* explicitly get done by exim4 if the target domain is in 
hubbed_hosts, or if exim4 has been told it is the local domain. The 
point is one wishes to PREVENT a DNS lookup that is doomed to fail, and 
one does so for machines that are not the machine-local domain by 
putting them in hubbed_hosts, which will cause exim4 to throw out a 
connection request for the local network infrastructure (starting with 
the network infra on the local machine) to handle, without doing an 
explicit DNS lookup. That is handled by /etc/hosts if it is populated, 
and by Avahi if it is present and /etc/hosts is not populated, and no 
doubt by a few other alternatives I am not familiar with as well. If 
none of them succeed, the delivery will fail, because if I recall 
correctly hubbed_hosts router config ends with no_more which prevents 
other routers having a go.

However, for domains NOT listed in hubbed_hosts, if not in smarthost 
mode, yes exim4's next move will be an explicit DNS lookup on the 
domain. It is trying to find out what *machine* it should contact to 
make the delivery to that domain. If it is in smarthost mode, it throws 
its hands in the air and passes the problem to the smarthost to solve.

Mark

Thread

Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-09-30 22:30 +0200
  Re: Configuring Exim for mail delivery Liam O'Toole <liam.p.otoole@gmail.com> - 2016-10-01 00:50 +0200
  Re: Configuring Exim for mail delivery Mark Fletcher <mark27q1@gmail.com> - 2016-10-01 04:00 +0200
    Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-01 12:40 +0200
      Re: Configuring Exim for mail delivery Brian <ad44@cityscape.co.uk> - 2016-10-01 13:30 +0200
        Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-01 13:50 +0200
          Re: Configuring Exim for mail delivery Clive Menzies <clive@clivemenzies.co.uk> - 2016-10-01 14:00 +0200
            Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-01 14:10 +0200
          Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-01 14:10 +0200
          Re: Configuring Exim for mail delivery Mark Fletcher <mark27q1@gmail.com> - 2016-10-01 14:10 +0200
      Re: Configuring Exim for mail delivery Mark Fletcher <mark27q1@gmail.com> - 2016-10-01 14:30 +0200
        Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-01 14:40 +0200
          Re: Configuring Exim for mail delivery Mark Fletcher <mark27q1@gmail.com> - 2016-10-01 15:00 +0200
            Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-01 15:00 +0200
        Re: Configuring Exim for mail delivery Brian <ad44@cityscape.co.uk> - 2016-10-01 15:00 +0200
          Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-01 15:10 +0200
          Re: Configuring Exim for mail delivery Mark Fletcher <mark27q1@gmail.com> - 2016-10-01 15:40 +0200
            Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-01 16:20 +0200
            Re: Configuring Exim for mail delivery Brian <ad44@cityscape.co.uk> - 2016-10-01 16:40 +0200
      Re: Configuring Exim for mail delivery Teemu Likonen <tlikonen@iki.fi> - 2016-10-01 16:00 +0200
        Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-01 16:20 +0200
  Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-01 11:10 +0200
    Re: Configuring Exim for mail delivery Brian <ad44@cityscape.co.uk> - 2016-10-01 12:10 +0200
      Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-01 12:40 +0200
      Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-01 14:10 +0200
        Re: Configuring Exim for mail delivery Brian <ad44@cityscape.co.uk> - 2016-10-01 14:30 +0200
          Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-01 14:30 +0200
            Re: Configuring Exim for mail delivery Mark Fletcher <mark27q1@gmail.com> - 2016-10-01 15:00 +0200
              Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-01 15:10 +0200
      Re: Configuring Exim for mail delivery Mark Fletcher <mark27q1@gmail.com> - 2016-10-01 14:10 +0200
    Re: Configuring Exim for mail delivery Mark Fletcher <mark27q1@gmail.com> - 2016-10-01 13:40 +0200
      Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-01 14:10 +0200
    Re: Configuring Exim for mail delivery rhkramer@gmail.com - 2016-10-01 14:20 +0200
      Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-01 16:30 +0200
    Re: Configuring Exim for mail delivery Liam O'Toole <liam.p.otoole@gmail.com> - 2016-10-01 18:30 +0200
      Re: Configuring Exim for mail delivery Brian <ad44@cityscape.co.uk> - 2016-10-01 20:20 +0200
        Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-01 22:50 +0200
          Re: Configuring Exim for mail delivery Brian <ad44@cityscape.co.uk> - 2016-10-02 00:30 +0200
            Re: Configuring Exim for mail delivery Mark Fletcher <mark27q1@gmail.com> - 2016-10-02 02:30 +0200
              Re: Configuring Exim for mail delivery Liam O'Toole <liam.p.otoole@gmail.com> - 2016-10-02 13:10 +0200
            Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-02 10:50 +0200
        Re: Configuring Exim for mail delivery Liam O'Toole <liam.p.otoole@gmail.com> - 2016-10-01 23:10 +0200
          Re: Configuring Exim for mail delivery Brian <ad44@cityscape.co.uk> - 2016-10-02 00:40 +0200
            Re: Configuring Exim for mail delivery Liam O'Toole <liam.p.otoole@gmail.com> - 2016-10-02 02:10 +0200
              Re: Configuring Exim for mail delivery Brian <ad44@cityscape.co.uk> - 2016-10-02 14:00 +0200
                Re: Configuring Exim for mail delivery Mark Fletcher <mark27q1@gmail.com> - 2016-10-02 14:50 +0200
                Re: Configuring Exim for mail delivery Gene Heskett <gheskett@shentel.net> - 2016-10-02 15:20 +0200
                Re: Configuring Exim for mail delivery Mark Fletcher <mark27q1@gmail.com> - 2016-10-02 15:50 +0200
                Re: Configuring Exim for mail delivery Brian <ad44@cityscape.co.uk> - 2016-10-02 15:40 +0200
                Re: Configuring Exim for mail delivery Liam O'Toole <liam.p.otoole@gmail.com> - 2016-10-02 17:30 +0200
      Re: Configuring Exim for mail delivery mo <mo777@gmx.net> - 2016-10-01 22:50 +0200

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