Re: [Exim] exim + smtp reverse dns

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Autor: Philip Hazel
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A: Nico Erfurth
CC: Eric Renfro, exim-users
Assumpte: Re: [Exim] exim + smtp reverse dns
On Fri, 20 Sep 2002, Nico Erfurth wrote:

> 1.) Very simple approach, just add
> host_reject_connection = +include_unknown


That will have no effect because "+include_unknown" applies to the
testing of any following item in the list. As there are no following
items in the list, Exim won't need to test anything, so +include_unknown
won't do anything. You would need to force it by something like

host_reject_connection = +include_unknown : non.existent.domain

Then Exim would try to look up the host name in order to test against
"non.existent.domain".

> 2.) the ACL way, exim provides us with
> <quote>
> $host_lookup_failed: This variable contains ``1'' if the message came
> from a remote host and there was an attempt to look up the host's name
> from its IP address, but the attempt failed. Otherwise the value of the
> variable is ``0''.
> </quote>


There's a catch there too. You have to make sure that Exim does attempt
a host lookup. You can do this by setting

host_lookup = *

> you could use this variable in an ACL (rcpt_acl) like this
>
> deny message = Sorry, your IP could not be looked up
>       condition = $host_lookup_failed

>
> The problem with this one is that it will permanent reject when you have
> DNS-Problems.


Indeed.

--
Philip Hazel            University of Cambridge Computing Service,
ph10@???      Cambridge, England. Phone: +44 1223 334714.