<div dir="ltr"><div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif">I totally concur on PTR = nice but not really trusted.</div><div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif">
<br></div><div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif">I can example it as being an accessory in determination of trust, though.</div><div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif">
<br></div><div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif">As a component of trust heuristics, on SMTP mailers that are 'first hop', some mailers look for a direct match between the MX and the A record returned for _HOSTNAME_ and the _HOSTNAME_ returned for the PTR on the in-addr.arpa for that A record when choosing to receive email or not from an unknown IP address.</div>
<div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif"><br></div><div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif">I said that all wierd, perhaps this says it better:</div>
<div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif"><br></div><div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif"><br></div><div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif">
chocolate-chunnel.example. IN MX 10 mx.chocolate-chunnel.example. (CALL THIS "A")</div><div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif">mx.chocolate-chunnel.example. IN A 1.2.3.4 (CALL THIS "B")</div>
<div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif"><br></div><div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif"><br></div><div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif">
4.3.2.1.in-addr.arpa. IN PTR mx.chocolate-chunnel.example. (CALL THIS "C")<br></div><div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif"><br></div><div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif">
<div class="gmail_default">IP of connecting Hostname of SMTP connection (CALL THIS "D")</div><div><div class="gmail_default"><div><div class="gmail_default">Hostname in HELO of SMTP session (CALL THIS "E")</div>
</div><div><div><div class="gmail_default">FQDN in FROM of SMTP session (CALL THIS "F")</div></div></div><div><br></div></div></div></div><div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif">
<br></div><div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif">Recipient MX would look at parity of these elements (ie D=A & E=F=B=C) </div><div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif">
<br></div>
<div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif">Spammers are typically lazy about rotating the hostname of sender and they don't make the carpet match the drapes and pillows, so to speak. If they all match, it impacts the heuristics.<br>
</div><div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif"><br></div><div class="gmail_default" style="font-size:small;font-family:verdana,sans-serif"><br></div><div class="gmail_extra"><div>
Jothan Frakes<br><a href="tel:%2B1.206-355-0230" value="+12063550230" target="_blank">+1.206-355-0230</a> tel<br><a href="tel:%2B1.206-201-6881" value="+12062016881" target="_blank">+1.206-201-6881</a> fax</div>
<br><br><div class="gmail_quote">On Tue, Mar 4, 2014 at 10:28 AM, Doug Barton <span dir="ltr"><<a href="mailto:dougb@dougbarton.us" target="_blank">dougb@dougbarton.us</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
The OP specifically said "anti-spam providers" in the context of "is there a risk that the target domain could be blacklisted by anti-spam providers?"<br>
<br>
I am assuming that everyone here (including the OP) knows that specific anti-spam solutions that you would run on your mail servers look for valid PTRs, but that would seem to be a different thing entirely from what the OP seems to be asking about.<br>
<br>
... so I revert to my original point, which is that it's hard to answer the OP's question intelligently without knowing more about what he's asking.<span><font color="#888888"><br>
<br>
Doug</font></span><div><div><br>
<br>
<br>
On 03/04/2014 10:06 AM, <a href="mailto:WBrown@e1b.org" target="_blank">WBrown@e1b.org</a> wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
Doug wrote on 03/04/2014 12:48:03 PM:<br>
<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
2. In my experience (which is not thorough, but also not zero) anti-spam<br>
</blockquote>
<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
folks are completely uninterested in what's in the PTR, and generally do<br>
</blockquote>
<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
not do any blacklisting by domain name in the sense you seem to mean.<br>
</blockquote>
<br>
Not exactly true. Many insist that there is a valid PTR record. Some<br>
care that it has a valid name, and that the forward lookup for that name<br>
matches.<br>
<br>
RBLs however, only look at IP address.<br>
<br>
<br>
<br>
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