'Blank' Emails received

[#1]

Hi
I have received a load of emails today which didn't get stopped by the spam filter. They had no readable 'From' or 'Subject' and were in multi-MIME format. Any reason why these didn't get picked up by the filter and don't have the normal postini headers?
Full Header here:
Return-path: <therese536sonia@poczta.onet.pl>
Envelope-to: x_wuefeigqh@XXXXXXX.co.uk
Delivery-date: Mon, 06 Oct 2008 13:51:14 +0100
Received: from exprod5mx194.postini.com ([64.18.0.40] helo=psmtp.com)
  by pih-sunmxcore14.plus.net with smtp (PlusNet MXCore v2.00) id 1KmpYP-0005tj-15
  for x_wuefeigqh@XXXXXXX.co.uk; Mon, 06 Oct 2008 13:51:13 +0100
Received: from source ([78.188.40.168]) by exprod5mx194.postini.com ([64.18.4.14]) with SMTP;
Mon, 06 Oct 2008 05:51:10 PDT
Message-ID: <2eea019dbf58$416e9af0$2a1dabd0@poczta.onet.pl>
From: "=?windows-1251?B?y8XOzcjE?=" <therese536sonia@poczta.onet.pl>
To: <x_wuefeigqh@XXXXXXX.co.uk>
Subject: =?windows-1251?B?WW91ciBhY3RpdmF0aW9uIGNvZGU=?=
Date: Mon, 06 Oct 3609 15:51:09 +0300
MIME-Version: 1.0
Content-Type: multipart/alternative;
boundary=----=_NextPart_000_0023_1D_BA3BBD85.B81DFDDC
X-Priority: 3
X-MSMail-Priority: Normal
X-Mailer: Microsoft Outlook Express 6.00.2900.2180
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180
X-pstn-neptune: 495/163/0.33/43
X-pstn-levels:    (S:62.74508/99.90000 CV:99.9999 )
X-pstn-settings: 1 (0.1500:0.1500) cv gt3 gt2 gt1
X-pstn-addresses: from <therese536sonia@poczta.onet.pl> [1368/71]
To:
X-PN-Virus-Filtered: by PlusNet MXCore (v4.00)
X-PN-Spam-Filtered: by PlusNet MXCore (v4.00)
Subject:

[#2]

Yes, I had five of these to my catch all email address, at 12:39pm, all using some sort of randomly generated email address.  Looking at them there must be very little for postini to go on?
I guess if this becomes regular I'm going to have to black hole my catch all email address.

[#3]

20 of them here

[#4]

I get these too. I suspect they're from the same guy who does the heavy breathing phonecalls.

[#5]

Hmm, I've not received any of these yet. I'll keep an eye out in the office for any reports coming in of this and see what I can find out from the headers posted in the first post when I get in tomorrow.

[#6]

I forwarded mine as attachments to Spamtraining if this helps?

[#7]

I get them from time to time, had a bunch this afternoon, all spam by the looks of it. Chris if you need any more headers let me know.

[#8]

I looked at the headers and found that they were all addressed to only 5 (supposedly random lettered) addresses.
E.g.
kjiwefiu3@username.f9.co.uk
deadr44@username.f9.co.uk
45fsef56@username.f9.co.uk
67h34gg@username.f9.co.uk
1234hsdf72@username.f9.co.uk

I went to the email settings redirections section, created 5 new redirections to blackhole them and have not had any since.
The apparent random nature of the addresses makes you think that it is not possible to trap them, but the addresses are repeated in later emails.