[Pkg-exim4-users] Reverse DNS lookups

[Andreas Metzler]

On 2006-05-29 Bill Horne <bill at horne.net> wrote:
> Andreas Metzler wrote:
> >On 2006-05-27 Bill Horne <bill at horne.net> wrote:
[...]
>> To make sure I understand you corectly: Given a IP-address you need to
>> check whether a A record for this IP exists?
>> 
>> Afaik that is impossible without reverse DNS, because this is exactly
>> the service reverse DNS provides.
[...]
> Given a domain name (received from a HELO)

The part about comparing HELO/EHLO and IP-address was missing

> and an IP address, I need to 
> know if Exim4 can do a *FORWARD* lookup and compare the IP address (if 
> any) shown for the domain name against the actual IP address the email 
> is being sent from.
[...]

You could use a dnsdb-lookup to get the A records for $sender_helo_name
and compare whether $sender_host_address matches any of these.

/usr/sbin/exim4 -be '${if match_ip{131.130.1.35}{${lookup dnsdb{>:a=mx.univie.ac.at}{$value}fail}}{yes}fail}'

(If the mail server is IPv6 connected this would get more complicated.)

Just an idea, hth, cu andreas
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