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Re: Reverse DNS and SMTP
- From: Jared Mauch
- Date: Thu Feb 28 15:55:43 2002
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.
> -----Original Message-----
> From: email@example.com [mailto:firstname.lastname@example.org] On Behalf Of
> Patrick Muldoon
> Sent: Thursday, February 28, 2002 1:15 PM
> To: email@example.com
> 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.
> Patrick Muldoon, Network/Software Engineer
> INOC, LLC
> Press Ctrl-Alt-Del now for IQ test.
Jared Mauch | pgp key available via finger from firstname.lastname@example.org
clue++; | http://puck.nether.net/~jared/ My statements are only mine.