RE: virus mail ignores MX?

["Burton M. Strauss III" <BStrauss () acm org>]

Read the relevant RFC (974)...

   The domain servers store information as a series of resource records
   (RRs), each of which contains a particular piece of information about
   a given domain name (which is usually, but not always, a host).  The
   simplest way to think of a RR is as a typed pair of datum, a domain
   name matched with relevant data, and stored with some additional type
   information to help systems determine when the RR is relevant.  For
   the purposes of message routing, the system stores RRs known as MX
   RRs. Each MX matches a domain name with two pieces of data, a
   preference value (an unsigned 16-bit integer), and the name of a
   host.  The preference number is used to indicate in what order the
   mailer should attempt deliver to the MX hosts, with the lowest
   numbered MX being the one to try first.  Multiple MXs with the same
   preference are permitted and have the same priority.

Emphasis on 'should', which has a specific meaning in RFCs - e.g.

   SHOULD    This word, or the adjective "recommended", means that there
             may exist valid reasons in particular circumstances to
             ignore this item, but the full implications MUST be
             understood and carefully weighed before choosing a
             different course.

> From the bad guy's perspective, wanting to get the mail through without
being filtered - in a perverse way - probably qualifies as a "valid
reason...to ignore this item".

-----Burton

> -----Original Message-----
> From: Monty Ree [mailto:chulmin2 () hotmail com]
> Sent: Friday, June 11, 2004 3:41 AM
> To: security-basics () securityfocus com
> Subject: virus mail ignores MX?
>
>
> Hello, all.
>
> I have some question about virus mail.
> I have set viruswall about my domain and all mails should be sent
> first to
> viruswall.
>
> xxxxx.com.               86400   IN      MX      0
> viruswall.xxxxx.com. <--
> viruswall
> xxxxx.com.               86400   IN      MX      5 mail.xxxxx.com     <--
> mail server
>
> When I see virus mail header, like below.
>
> Received: from test.com ([211.117.47.1])
>       by mail.xxxxx.com (8.11.6/8.11.6) with ESMTP id i5B8DdW02504
>       for <chulmin2 () xxxxx com>; Fri, 11 Jun 2004 17:13:44 +0900
>
> some virus mails are filtered well at viruswall.
> but other virus mails are not get through viruswall,
> and go directly to mail.xxxxx.com. I think.
>
> so I think some virus mail ignores MX, right?
>
> What's the problem and how can I solve this problem?
>
>
> Thanks in advance.
>
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Attend a course taught by an expert instructor with years of in-the-field 
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