Preventing DNS lookup prior to sending 220 banner in exim4 on etch
On Tue, Jun 17, 2008 at 08:32:15PM +0200, email@example.com wrote:
> On Tue, Jun 17, 2008 at 01:37:59PM -0300, Eduardo M KALINOWSKI wrote:
> > On Tue, 17 Jun 2008 17:34:02 +0200, firstname.lastname@example.org
> > (email@example.com) 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.