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Eduardo M KALINOWSKI 06-17-2008 04:37 PM

Preventing DNS lookup prior to sending 220 banner in exim4 on etch
 
On Tue, 17 Jun 2008 17:34:02 +0200, chris+lists@chrissearle.org
(chris+lists@chrissearle.org) wrote:

I have exim4 (exim4-daemon-heavy) running on etch.

This machine has only a few users who send directly. One of them has
an ISP who seems to have a broken DNS setup.

The symptom I see is that when this user connects to the server (port 25
or 587) there is a large delay before the 220 banner is shown e.g.:

[snip]

Is it possible to whitelist a range or turn off the check?


There is a debconf option that minimizes DNS lookups. It should solve
this problem, but it might disable the lookups also in places where
you might want them.


In any case, you can change the value of that option with
dpkg-reconfigure exim4-config or by editing
/etc/exim4/update-exim4.conf.conf .


--
Eduardo M KALINOWSKI
eduardo@kalinowski.com.br


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Andrew Sackville-West 06-17-2008 07:20 PM

Preventing DNS lookup prior to sending 220 banner in exim4 on etch
 
On Tue, Jun 17, 2008 at 08:32:15PM +0200, chris+lists@chrissearle.org wrote:
> On Tue, Jun 17, 2008 at 01:37:59PM -0300, Eduardo M KALINOWSKI wrote:
> > On Tue, 17 Jun 2008 17:34:02 +0200, chris+lists@chrissearle.org
> > (chris+lists@chrissearle.org) wrote:
> > >I have exim4 (exim4-daemon-heavy) running on etch.
> > >
> > >This machine has only a few users who send directly. One of them has
> > >an ISP who seems to have a broken DNS setup.
> > >
> > >The symptom I see is that when this user connects to the server (port 25
> > >or 587) there is a large delay before the 220 banner is shown e.g.:
> > >
> > >[snip]
> > >
> > >Is it possible to whitelist a range or turn off the check?
> >
> > There is a debconf option that minimizes DNS lookups. It should solve
> > this problem, but it might disable the lookups also in places where
> > you might want them.
>
> OK - just tried that. Seems to set the host_lookup to empty instead of *
> and yes - the 220 banner is now instant.
>
> I wonder if there is a way to say that host_lookup is everything except
> a range though? It would be great to be able to say all hosts except the
> IPs in this ISP's dial up ranges.

I think you can do that directly in the exim.conf file, but that would
more or less require a handwritten file. It's not that hard, but
definitely an order of magnitude more difficult than using
debconf. There may be a way to add additional lines to the debconf
config as well, which would help. You should read the exim
documentation (heh) for more details.

A


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