domain blocking for DNS

[admin at kclinux.net]

A lot of e-mail servers are bouncing emails that does not have a reverse
DNS.  Yahoo (I think) was the first and a lot soon started after.  I think
even Earthlink or Mindspring is doing the same thing.  I've also had 3
clients that had this problem.  They all either have business DSL or a T3.
The T3 getting configured to have reverse DNS was no problem.  The DSL
provider (which I wont mention right now since this has turned into a
breached contract between my client and the ISP) wouldn't set the static
IP's to have reverse DNS due to "security issues".  I also had this told to
me one time by a hosting company in Raytown - IMMe.Net (which seems of went
bankrupt or lost their domain name) and I soon took my collocated servers
and got a refund.  

After almost a week, I'm still waiting for the ISP's my clients use to give
me documentation or a link to the security vulnerabilities that reverse DNS
causes.  

Does anyone here know of any?

-----Original Message-----
From: owner-kclug at marauder.illiana.net
[mailto:owner-kclug at marauder.illiana.net] On Behalf Of Hanasaki JiJi
Sent: Thursday, May 08, 2003 11:28 AM
To: List - KCLUG
Subject: domain blocking for DNS

Adding a parallel thread to "domain blocking due to spam".

Some of you might have noticed a msg sent to me via the list becuase the 
sender was being bounced when sent directly.  I recently added a 
configuration to my mailserver to reject connections from sources that 
do not have forward/reverse DNS setup.

This resulted in alot of rejections from ligitimate companies and 
induviduals!  It was put into place becuase some spam seems to come from 
telnet sessions on an IP that has no DNS / ReverseDNS entry.

Do you folks think it is reasonable to expect admins to have both DNS 
and ReverseDNS propperly configured?  at least for their outgoing 
mailserver?

Thanks