Hi, Andy -
A vague memory stirs…
Check the *Exim Specification* in the *String Expansions* chapter and see
the text for the *$host_lookup_deferred* variable. There you'll read
(emphasis mine):
Looking up a host’s name from its IP address consists of more than just a
single reverse lookup. *Exim checks that a forward lookup of at least one
of the names it receives from a reverse lookup yields the original IP
address. If this is not the case, Exim does not accept the looked up
name(s)*, and $host_lookup_failed is set to “1”. Thus, being able to find a
name from an IP address (for example, the existence of a PTR record in the
DNS) is not sufficient on its own for the success of a host name lookup. If
the reverse lookup succeeds, but there is a lookup problem such as a
timeout when checking the result, the name is not accepted, and
$host_lookup_deferred is set to “1”. See also $sender_host_name.
Thank you for not obfuscating the IP address, by the way… It meant I could
check both reverse and forward lookups for you, and find that although you
have a reverse lookup:
% nslookup 93.191.32.251
Server: 144.32.128.242
Address: 144.32.128.242#53
Non-authoritative answer:
251.32.191.93.in-addr.arpa name = asigra2.ldex.co.uk.
Authoritative answers can be found from:
32.191.93.in-addr.arpa nameserver = ns1.pingnetworks.co.uk.
32.191.93.in-addr.arpa nameserver = ns2.pingnetworks.co.uk.
ns1.pingnetworks.co.uk internet address = 93.191.32.131
ns2.pingnetworks.co.uk internet address = 93.191.32.146
you don't seem to have a forward lookup:
% nslookup asigra2.ldex.co.uk
Server: 144.32.128.242
Address: 144.32.128.242#53
** server can't find asigra2.ldex.co.uk: NXDOMAIN
So I'd guess this might be causing Exim to flag its reverse lookup as
having failed?
Cheers,
Mike B-)
On 10 June 2016 at 08:56, <a.smith@???> wrote:
> Hi,
>
> I'm running Exim 4.86.2 on FreeBSD 9.3 and I'm having an issue whereby
> it is registered incoming mails as originating from hosts without an rDNS
> record, but they do have an rDNS record. I've just enabled the
> X-Host-Lookup-Failed ACL to add the extra header and it confirms what I was
> seeing by enterpreting the "Recieved:" header.
>
> For example when sending from 93.191.32.251 I see:
>
> X-Host-Lookup-Failed: Reverse DNS lookup failed for 93.191.32.251 (failed)
>
> and
>
> Received: from [93.191.32.251] (port=49828 helo=asigra2.ldex.co.uk)
>
>
>
> but nslookup from the mail server itself provides:
>
> nslookup 93.191.32.251
> Server: 8.8.8.8
> Address: 8.8.8.8#53
>
> Non-authoritative answer:
> 251.32.191.93.in-addr.arpa name = asigra2.ldex.co.uk.
>
>
>
> Any clues as to why Exim is failing when nslookup/dig from the same host
> using the same DNS server work?
>
>
>
> thanks in advance, Andy.
>
>
>
>
>
>
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