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Reverse DNS doesn't work

Printed From: LogSat Software
Category: Spam Filter ISP
Forum Name: Spam Filter ISP Support
Forum Description: General support for Spam Filter ISP
URL: https://www.logsat.com/spamfilter/forums/forum_posts.asp?TID=2423
Printed Date: 19 January 2026 at 1:29am


Topic: Reverse DNS doesn't work
Posted By: Guests
Subject: Reverse DNS doesn't work
Date Posted: 17 November 2003 at 3:35pm

I have reverse DNS set to reject if there is no reverse DNS.  As you can see from the logs below (email and ips changed) but it accepts the connection runs a reverse dns lookup and comes up wtih it being a comcast.net address which is a cable modem address.  It does not reject the connection however it accepts it despite the fact that the domain sending the email is different then what it found in the reverse DNS lookup.  What am I missing??

thankyou, Josh

11/17/03 14:18:01:062 -- (352) Connection from: 68.44.129.35  -  Originating country : United States
11/17/03 14:18:01:562 -- (352) Resolving 68.44.129.35 - pcp086361pcs.audubn01.nj.comcast.net
11/17/03 14:18:01:562 -- (352) Mail from: mailto:bob@bob.com" CLASS="ASPForums" TITLE="WARNING: URL created by poster. - bob@bob.com
11/17/03 14:18:07:718 -- (352) - MAPS search done... .
11/17/03 14:18:07:718 -- (352) RCPT TO:  mailto:tom@john.net" CLASS="ASPForums" TITLE="WARNING: URL created by poster. - tom@john.net accepted
11/17/03 14:18:07:890 -- (352) EMail from 11/17/03 14:18:01:062 -- (352) Connection from: 68.44.129.29  -  Originating country : United States
11/17/03 14:18:01:562 -- (352) Resolving 68.44.129.35 - pcp086361pcs.audubn01.nj.comcast.net
11/17/03 14:18:01:562 -- (352) Mail from: mailto:bob@bob.com" CLASS="ASPForums" TITLE="WARNING: URL created by poster. - bob@bob.com

11/17/03 14:18:07:718 -- (352) - MAPS search done... .
11/17/03 14:18:07:718 -- (352) RCPT TO:  mailto:tom@john.net" CLASS="ASPForums" TITLE="WARNING: URL created by poster. - tom@john.net  accepted
11/17/03 14:18:07:890 -- (352) EMail from mailto:bob@bob.com " CLASS="ASPForums" TITLE="WARNING: URL created by poster. - bob@bob.com   to  mailto:tom@john.net" CLASS="ASPForums" TITLE="WARNING: URL created by poster. - tom@john.net was queued. Size: 1 KB


Replies:
Posted By: LogSat
Date Posted: 17 November 2003 at 10:49pm

Josh,

The reverse DNS simply checks to see if there is a PTR record associated with that IP address. The fact that the reverse DNS does not match with the email address is perfectly normal. We have a mail server that handles about 8,000 domains. However the SMTP server is of course using a single IP. The reverse DNS for that IP resolves to a specific domain. But the other 7,999 domains are also using that IP, and then "they" send emails out, the reverse dns of course won't match.

What could be done however is to, once retrieved the reverse DNS, ping that name to see if it actually matches the originating IP. Since it's very easy to setup fake reverse DNS entries, this would catch all fake entries. This feature is on our wish list, and will be implemented soon.

Roberto F.
LogSat Software


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