[Mimedefang] Fw: [Sare-users] Spam with numbers in subj and b ody

[Steffen Kaiser]

On Tue, 6 Jun 2006, Joseph Brennan wrote:

>
>
> --On Wednesday, June 7, 2006 12:23 PM +1000 Stewart <mimedefang at f8.com.au> 
> wrote:
>
>> if ($MessageID =~ /<[a-z]+\@(columbia|COLUMBIA)/)
>
> No!  For one thing just plain domain.com could be a hostname.  But
> also, the Message-ID is not required to contain a hostname.
>
> The format of Message-ID (see RFC 2822) boils down to "<", string,
> "@", string, ">".  Therefore a Message-ID <abcdefg at columbia.edu> is
> properly formed as per the standard.
>
> However the purpose of Message-ID is to be a unique identifier, and
> by ancient practice this is done by putting the sender's hostname in
> the second string and something usually involving a timestamp in the

A practice RECOMMENDED by RFC2822 section 3.6.4. Even further "The message 
identifier (msg-id) itself MUST be a =>globally unique identifier<= for a 
message." To put another domain's name into a message ID is certain 
failproof for _not_ generating a globally unique ID.

> first string.  As a result we don't expect to see "columbia.edu" as
> the second string, nor all small letters in the first string, so we
> can reject on that.[*]

You've blocking any host of spaceship enthusiasts as well, unless you 
anchor 'columbia' to the end of the string somehow.


> [* In fact all small letters in the first string is never generated
> by any legit mail client or server that I know of, so you could reject
> on just simply:
>   if ($MessageID =~ /<[a-z]+\@>/)
> But there is at least one server, mailcity.com, that generates all

Found some legal mails from mshome.net and MSK.SU that use [:alpha:]+ on 
the lefthand side. However, you've put the '>' in the pattern in error, 
right?

> capital letters in its first string.  I don't know how this gets them
> unique Message-IDs.]

Once you have an unique ID, you can represent it with any (legal) 
characters you like, can't you? E.g. radix 26 with the "digits" a through 
z. :)

Bye,

-- 
Steffen Kaiser