[Mailman-Users] Hotmail - Sender appears as (Unknown) and (No Subject) line

[Pearl & Dean Newsletter]

Having a problem with Mailman and Hotmail.

The sender appears as (Unknown) and the subject line simply says (No 
Subject).

All other e-mail providers are fine and show the correct Sender and 
Subject line.

We are sending out a HTML Newsletter to a database of 15,000 people.

Here is the Message Header from the Hotmail recieved e-mail (I've 
removed our email details, IP etc to hide our privacy):

x-store-info:sbevkl2QZR7OXo7WID5ZcaZ0jeT0hTF67wC3GlgJLKuNX2JLoVmz6SozALo6vOlfS+MPHBYgjfNdgHNtL6Oj1VzhHVVE6jS52YXoHY6PIlfBFuk8eyRTUDPdrbApHJX+8v6Mqf+6hTU=
Authentication-Results: hotmail.com; sender-id=none (sender IP is 
46.17.90.138) header.sender=E-MAIL REMOVED; dkim=none; x-hmca=none
X-SID-PRA: E-MAIL REMOVED
X-DKIM-Result: None
X-Message-Status: n:0:n
X-SID-Result: None
X-AUTH-Result: NONE
X-Message-Delivery: Vj0xLjE7dXM9MDtsPTA7YT0wO0Q9MTtHRD0xO1NDTD0w
X-Message-Info: 
J97kXdVaP39U+I3F4qoyky3fsu0kb0eo4+2S6uZvFiMMmAPn3sBWpjtm43bSEx8uJBfBauawku0M8ahba85gims9RAWiQ1Se5C0/TaFlGEW9YMu3mTiiNr1NdRT7k/UfHBCkzx4TC2wJ2my7h3/MLA==
Received: from E-MAIL REMOVED ([46.17.90.138]) by 
SNT0-MC2-F29.Snt0.hotmail.com with Microsoft SMTPSVC(6.0.3790.4900);
      Fri, 20 Apr 2012 09:03:35 -0700
X-No-Auth: unauthenticated sender
X-No-Auth: unauthenticated sender
X-No-Auth: unauthenticated sender
X-No-Auth: unauthenticated sender
X-No-Auth: unauthenticated sender
Received: from E-MAIL REMOVED (mail.pearlanddean.com [IPv6:::1])
     by E-MAIL REMOVED (Postfix) with ESMTP id AE0BDC22AE;
     Fri, 20 Apr 2012 17:04:43 +0100 (BST)
X-No-Relay: not in my network
Received: from P0010101 (83-244-245-26.cust-83.exponential-e.net
     [83.244.245.26])
     by E-MAIL REMOVED (Postfix) with ESMTPA id 67DA8BFE58
     for <E-MAIL REMOVED>;
     Fri, 20 Apr 2012 17:04:31 +0100 (BST)
From: <E-MAIL REMOVED>
To: <E-MAIL REMOVED>
Subject: Lockout,
     Salmon Fishing In The Yemen & more! Competition & Picture Quiz!
Date: Fri, 20 Apr 2012 17:10:39 +0100
Message-ID: <F00845961A5C487C894477B1B2CA384A at pd.int>
MIME-Version: 1.0
Content-Type: multipart/alternative;
     boundary="----=_NextPart_000_0000_01CD1F18.82B887A0"
X-Mailer: Microsoft Office Outlook 11
Thread-Index: Ac0fECC4kM+iNJZaSzuBDMDrAJjp1g==
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5931
X-BeenThere: E-MAIL REMOVED
X-Mailman-Version: 2.1.12
Precedence: list
Reply-To: E-MAIL REMOVED
List-Id: <E-MAIL REMOVED>
List-Unsubscribe: <http://URL REMOVED>,
<mailto:E-MAIL REMOVED?subject=unsubscribe>
List-Archive: <URL REMOVED>
List-Help: <mailto:E-MAIL REMOVED>
List-Subscribe: <URL REMOVED,
<mailto:E-MAIL REMOVED>
Sender: E-MAIL REMOVED
Errors-To: E-MAIL REMOVED
Return-Path: E-MAIL REMOVED
X-OriginalArrivalTime: 20 Apr 2012 16:03:37.0161 (UTC) 
FILETIME=[2522A390:01CD1F0F]

This is a multi-part message in MIME format.

------=_NextPart_000_0000_01CD1F18.82B887A0
Content-Type: text/plain;
     charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable