From: vjs@calcite.rhyolite.com
In article ,
Barry Margolin wrote:
>Sometimes companies put useless A records on their domain name as an
>anti-spam measure. I think there are some spambots that send to the A
>record rather than the MX record, so putting 0.0.0.0 or 127.0.0.1 in the
>A record will prevent them from sending to you.
It will also trigger spam defenses in many SMTP servers (mail
receivers) to refuse mail from domain names that resolve to bogus
IP addresses. Domains that can't receive a bounce (NDR) shouldn't
be sending any mail. (Never mind that bounces must be avoided today
to minimize spam backscatter.)
>Another strange thing you see sometimes is an MX record that points to
>".". Companies do this to indicate explicitly that mail shouldn't be
>sent to that domain. If they leave out the MX record, mail senders will
>fall back to the A record, and they don't want all those useless SMTP
>connection attempts.
An MX record of "." to say "no mail here" is not very strange. I think
it's sanctioned by an RFC, but am too lazy to craft an grep pattern to
find the text. Or maybe the sanctioned tactic is a record of "" (null).
It makes sense to use a bogus MX RR of "." , but not to avoid useless
SMTP connection attempts. Any IP address that appears in a noticable
A record will get far more and more expensive noise than TCP SYNs to
port 25.
Given the various DNS records for tigers.com.au, www.tigers.com.au, and
mail.tigers.com.au, the explanation that makes most sense to me is a
combination of inattention or confusion (e.g. about the cost of SYNs)
and a lack of major bad effects. They doubtless losing some hits on
their www.tigers.com.au pages and so perhaps a few ticket sales by
not having at least an HTTP redirection from tigers.com.au to
www.tigers.com.au.
Vernon Schryver vjs@rhyolite.com
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