Hi Xaver,

I had a similar problem when I set up the mail server on
my virtual server and wanted to send mail to domains that
are hosted by zoneedit.com.

After searching a while, I think this is the way how it works:

Step 1:
Bluewin does a reverse DNS lookup on your IP (,
which returns the following:

# nslookup
;; Truncated, retrying in TCP mode.
Server:         www.multipop.ch.
Address:     name = mailhost.aa795.ch.     name = mailhost.aerni.net.     name = mailhost.bar16.ch.     name = mailhost.sysop.ch.     name = mailhost.zingg.org.     name = mailhost.satshop.cc.     name = mailhost.aquacare.ch.     name = mailhost.glaettli.cc.     name = mailhost.multipop.ch.     name = mailhost.satshops.ch.     name = mailhost.spacebbs.ch.     name = mailhost.amigaland.ch.     name = mailhost.augsauger.ch.     name = mailhost.begegnung.ch.     name = mailhost.satvision.ch.     name = mailhost.hackernews.ch.ch.     name = mailhost.natel-news.ch.     name = mailhost.satanlagen.ch.     name = mailhost.satantennen.ch.     name = mailhost.wiso-schoch.ch.     name = mailhost.xariffusion.ch.     name = mailhost.sat-receiver.ch.     name = mailhost.estherundpetr.ch.     name = mailhost.luisenstrasse.ch.     name = mailhost.arthurandersen.ch.     name = mailhost.elektronik-news.ch.     name = mailhost.zuerichsee-gastro.ch.     name = mailhost.pop.ch.     name = mailhost.rtv.ch.     name = mailhost.dsng.ch.

Step 2:
Bluewin does a "normal" forward DNS lookup, using the result from the
above query. The forward (A) query has to match your IP address, otherwise
Bluewin will complain about the PTR record.

However, the above query returned more than one value, so I am
not sure which host is used for the lookup - I guess that just
the first host is taken. Since the order is random, you cannot
say anything reliable about which host will be used for the lookup.
Maybe it even fails directly if the response is not unique - I don't

When I tried the lookup the first time, mailhost.aquacare.ch was used
for the query. However, mailhost.aquacare.ch does not exist (even the
domain does not exist), so the lookup fails and rightly so Bluewin
complains about your PTR record.

I think the purpose of this reverse and forward DNS lookup procedure is
to prevent spam, since most spam comes from hacked machines (mostly from
dynamic IP address ranges) which do not have correct PTR records - just
as it is the case with your machine ;-)

Gruass, Franco

Adrian Ulrich wrote:
Good Morning,

Is your source ip ?


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Xaver Aerni wrote:
Our System receive ex. This MSG

The original message was received at Tue, 25 Mar 2008 16:20:47 +0100 from 
localhost []

   ----- Transcript of session follows ----- ... while talking to 
<<< 451 No thanks. (How about PTR records?) ... while talking to 
<<< 451 No thanks. (How about PTR records?) ... while talking to 
<<< 451 No thanks. (How about PTR records?) <[EMAIL PROTECTED]>... Deferred: 
451 No thanks. (How about PTR records?)
Warning: message still undelivered after 4 hours Will keep trying until message 
is 5 days old

Xaver Aerni
Z├╝richstrasse 10a
8340 Hinwil
Tel. 001 707 361 68 39

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