Spam from two letter domain.

[Budi Febrianto]

Dear all,

Recently I got hit by spam that came only from two letter domain, like 
xi.com, cn.com, gr.com and many others.
Right now it only got hit by this rules
4.00    BAYES_80                Bayesian spam probability is 80 to 95%
1.90    INVALID_MSGID    Message-Id is not valid, according to RFC 2822
0.39    SARE_RECV_SPAM_NAME2    

Right now I only put many of those two letter domains in our blacklist, 
but I'm affraid that will come many more with different domain.

This is one example of the email
 >>>>>
Return-Path: <<81>g>
Received: from mn.com (n219076186134.netvigator.com [219.76.186.134])
        by mail.busanagroup.com (8.13.8/8.13.8) with ESMTP id n2P4CHlP022256
        for <Rakesh at busanagroup.com>; Wed, 25 Mar 2009 11:12:34 +0700
Date: Wed, 25 Mar 2009 12:12:52 +0800
From: Milla <pemdb2004 at mn.com>
X-Mailer: cxaz 0.415
Reply-To: pemdb2004 at mn.com
X-Priority: 3 (Normal)
Message-ID: 2818841884.905474100 at mn.com
To: Rakesh at busanagroup.com
Subject: Good afternoon! I Milla
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit

Good afternoon! I Milla Look my photo, call me and fuck me bjqxhp: 
http://t-tnov.mail15.su iqylrxcz

 >>>>>

It is safe to block all the two letter domains?
Or is there any other rules to block this kind of spam?

I'm using
MailScanner 4.65.3

Thanks in advance.