[Wolves] Exim sender verify problem

Adam Sweet adam at adamsweet.org
Tue Oct 9 20:18:17 BST 2007


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Wayne wrote:

> That still hasn't solved it, it fact its worse!
> I now get R=dnslookup defer (-1) host lookup didnot complete
> and retry timout exceeded
> VERY quickly and its bounced back to me.
> 
> I wonder whether its because although the domain pings to 85.92.73.96,
> the email server listed in the MX
> record is at 195.74.102.146 and has no reverse dns?

Can you paste in the actual output from Exim's logs. I can't follow
what's happening.

Pinging is of no use to you, a lot of people block pings, what you are
getting out of it though is DNS resolution of hostname to IP address.
Try telnetting the mail server on the other end on port 25 though the
fact that you can send mail to it from yahoo says that it's accepting mail.

- From here a lookup on the MX record says:

adam at elmo:~$ dig remail-ltd.co.uk mx

<snip>

;; ANSWER SECTION:
remail-ltd.co.uk.       14186   IN      MX      0 remail-ltd.co.uk.

<snip>

;; ADDITIONAL SECTION:
remail-ltd.co.uk.       14186   IN      A       85.92.73.96

A forward lookup on remail-ltd.co.uk is as shown above. A reverse lookup
 on this IP address gives:

adam at elmo:~$ dig -x 85.92.73.96

<snip>

;; ANSWER SECTION:
96.73.92.85.in-addr.arpa. 3054  IN      PTR
server4.discountdomainsuk.com.

All of which looks pretty above board to me, apart from the fact that
some people will refuse your mail if you forward lookup and reverse
lookup don't match, but I guess this a problem with shared servers.

However I've no idea where you're getting 195.74.102.146 from. Which is
interesting because we have an IP range at work which is almost
identical to the range this address is in and I happen to know that that
range belongs to Enta, an ISP in Telford. And they broke our reverse DNS
and I've been hammering them all day about it, though a quick check
shows they've fixed mine now.

In fact, this IP resolves to dns-cache1.enta.net so it may be that they
fixed my DNS and broke yours :) Are you on Enta? If so it looks like
they have broken your DNS.

Try the same commands yourself on your mail server to make sure your
output makes sense and the results are consistent with each other and
with mine. I'm using my dad's Plus.net DNS at the mo. You can also
compare against the output you get from using OpenDNS as below and take
a look at http://www.dnsstuff.com/ too.

If your DNS is indeed b0rked, you could try using OpenDNS for a while:

http://www.opendns.com/

they're DNS servers are listed at the bottom.

Other than all this, you could try:

exim -qff

which will force Exim to attempt delivery of everything in your mail
queue, which you can watch in a different terminal by doing

tail -f /var/log/exim/main.log

or whatever your Exim log file is. The output should point you at the
fact that the reverse DNS lookup is failing when receiving from them and
so you are sending them a temporary local error and when you are
attempting to send to them, you're sending to the wrong place.

...Or some of other concoction of DNS weirdness which is happening at
your end.

Regards,

Adam Sweet - DNS Inspector :)

- --

http://blog.adamsweet.org/

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