Re: Reverse DNS and SMTP

[Nicole Harrington <nmh () daemontech com>]

 Hi
 Does anyone know of a program that can flag such things and alter mail headers
on the fly like this?


  Nicole


On 28-Feb-02 Unnamed Administration sources reported Jared Mauch said :
> On Thu, Feb 28, 2002 at 01:35:09PM -0700, Daniel Lark wrote:
> > You are most correct, it is definitely a double edged sword. Let's say
> > you try to reverse DNS on an address who's nameserver is down or
> > otherwise unreachable, what then? Some admins I know deliberately do run
> > reverse DNS as they view it as system cracker tool, or they feel it is
> > an unwarranted load, RFCs be damned. Is this admin decision the fault of
> > the user?
>
>       Use a non clueless isp.  the market is fairly saturated in
> most places with service providers.
>
> > You are not first one to try this. I have tried this myself and a
> > financial type didn't get an important email because of it. You know the
> > rest of the story.
>
>       What I do is format my smtp headers such that a very simple
> regex can find mail with no reverse dns and dump it in a spam folder.
> I find this catches a lot of the messages.
>
>       I try and let people know but for example, I am unable to
> find anyone at American Express or NWA that can fix their dns.
> (others are prompt in fixing their dns problems).
>
> > A better solution is to check the ip and see if it is an MX record for
> > the domain the mail purports to be from.
>
>       This has a number of flaws.  I won't delve into them though.
>
> > Just my opinion, and I could wrong.
>
>       - Jared
>
> > -dan
> >
> > -----Original Message-----
> > From: owner-nanog () merit edu [mailto:owner-nanog () merit edu] On Behalf Of
> > Patrick Muldoon
> > Sent: Thursday, February 28, 2002 1:15 PM
> > To: nanog () merit edu
> > Subject: Reverse DNS and SMTP
> >
> >
> >      We have recently implemented a policy on our mail servers of not
> > accepting mail from hosts that do not correctly resolve via reverse DNS.
> > While we on the technical side love the idea, there have been some
> > questions from the business side of the house.  
> >
> >      If an ISP who doesn't have reverse DNS setup correctly on their
> > mail servers, we point them to the RFC's and generally offer to help
> > them correct it.  
> >      We have noticed that our spam has reduced drastically, and the
> > complaints are few, but alas this is a double edged sword, where if you
> > even block 1 legitimate e-mail out of the 100K+ that we receive daily,
> > someone is going to complain.   
> >
> > Just curious if anybody here is doing the same and the response that
> > they have had from doing so.  Replies off list are fine and I will
> > summarize if people are interested.  
> >
> > Thanks, 
> > Patrick
> >
> > --
> > Patrick Muldoon, Network/Software Engineer
> > INOC, LLC
> > doon () inoc net
> >
> > Press Ctrl-Alt-Del now for IQ test.
>
> -- 
> Jared Mauch  | pgp key available via finger from jared () puck nether net
> clue++;      | http://puck.nether.net/~jared/  My statements are only mine.



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