[Dshield] DNS MX record block question

Jon R. Kibler Jon.Kibler at aset.com
Sun Sep 7 21:31:15 GMT 2003


Johannes Ullrich wrote:
> 
> The "MX record" part of this disucssion was ok. But it got a bit of
> track into the overall "what is spam" territory.
> 
> So a few opinions about MX records, spam and filtering:
> 
> (*) Every domain that is used as part of a 'From:' address,
>     should have a valid MX record. Otherwise, nobody would
>     be able to respond.
<SNIP!>

Johannes,

I agree with everything you said, except for your first point. You happen to be technically incorrect for two reasons.
   1) Major reason: You can send email to a system without it having an MX record. Please see my Friday post for an explanation why.
   2) Minor reason: The 'From:' header is not often not relevant because:
      a) It is often superseded by other headers, such as 'Reply-To:', especially on mailing lists.
      b) It says little about who actually sent the message. In legitimate email, the real sender is defined by the "Envelope Sender."

Anyway, I just wanted to make sure that the point that systems to NOT have to have an MX record to receive email is clarified.

Thanks!

Jon R. Kibler
A.S.E.T., Inc.
Charleston, SC  USA




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