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List:       exim-users
Subject:    Re: [EXIM] Question with fallback_hosts and DNS timeouts
From:       David Shaw <dshaw () jabberwocky ! com>
Date:       1998-05-29 22:36:01
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On Fri, May 29, 1998 at 06:26:05PM -0400, David Shaw wrote:
> Hi all,
> 
> I am running 1.92 with fallback_hosts enabled.  It works fine, except in
> one circumstance - if a receipent's host cannot be looked up at all due to
> the DNS just timing out (i.e. no answer either positive or negative) the
> message is not sent to the fallback host.  It is instead kept in the
> queue.
> 
> If the DNS succeeds but the host is not available (times out or connection
> refused), then fallback_hosts does work. 
> 
> Is this correct behavior?  I would think that if a message couldn't be
> delivered for *any* reason it would go to the fallback host.. 
> 
> On further thought, I guess the problem is that since fallback_hosts is in
> the SMTP transport, and the DNS failure is happening in the lookuphost
> router, the message never progresses to the transport level.
> 
> I wonder if something could be done with pass_on_timeout and a different
> router following lookuphost to just blindly forward the mail elsewhere.

And after I sent that, I came up with this:

lookuphost:
  driver = lookuphost
  transport = remote_smtp
  pass_on_timeout

fallback:
  driver = domainlist
  transport = remote_smtp
  route_list = "* my.fallback.host byname"

David

-- 
    David Shaw  |  dshaw@cs.jhu.edu  |  WWW http://www.cs.jhu.edu/~dshaw/
+---------------------------------------------------------------------------+
   "There are two major products that come out of Berkeley: LSD and UNIX.
      We don't believe this to be a coincidence." - Jeremy S. Anderson

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