[Mimedefang] Potential for Business mail servers to not havereverse DNS

Joseph Brennan brennan at columbia.edu
Fri Sep 22 12:11:11 EDT 2006

--On Friday, September 22, 2006 8:37 -0700 John Rudd <john at rudd.cc> wrote:

> * A PTR record for its IP address ("the connecting IP address").  Failure
> leads to a temporary rejection of the message.
> * The PTR record must resolve to a name which is they key for an A
> record.  Failure leads to a temporary rejection of the message.
> * The A record must have at least 1 IP address which matches the
> connecting IP address.  Failure leads to a permanent failure of the
> message.
> * The name from the PTR record must not look dynamic.  Failure is a
> permanent rejection of the message.
> * The above restrictions can be avoided via SMTP-AUTH.
> I have yet to find out that any such rejection was a valid email message.

I happen to be logging all missing RDNS, accepted or not.  Within 30
minutes we saw the following on one host of five.  The first 3 have no PTR. 

The other 2 have nonmatching forward and reverse.

IP			domain in the sender address (my comment)		reuters.com (news)		mailer-relay.sportsline.com (sports news)		indiaclub.com (online vendor)		weforum.org (nonprofit org)		lists.kabissa.org (nonprofit org)

Joseph Brennan
Columbia University Information Technology

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