Merkwürdige Anzeige von Email

ich bin jetzt auf Tunderbird umgestiegen und bin begeistert.
Allerdings ahabe ich ein (hoffentlich) kleines Problem:

Einige Emails werden bei mir sehr merkwürdig formatiert angezeigt.
Kann mir da jemnad helfen?
die Mails sehen etwa so aus:

<style type="text/css">BODY, TD {font-family: verdana,arial,helvetica,sans-serif;font-size: 12px;color: #000000;}

LI {line-height: 120%;}
UL.smallBorder {margin:10px 5px 10px 20px;}
LI.smallBorderLi {margin:0px 0px 5px 0px;}
UL.Narrow {margin:10px 5px 0px 40px;}
HR.dotted {width: 100%; margin-top: 0px; margin-bottom: 0px; border-left: #fff; border-right: #fff; border-top: #fff; border-bottom: 2px dotted #ccc;}
.smallEmphasis {font-family: verdana,arial,helvetica,sans-serif;font-size: 11px;font-weight: bold;color: #000000;}
.serifBig {font-family: serif;font-size: 20px;font-weight: bold;color: #000000;}
.serif{font-family: serif;font-size: 16px;color: #000000;}
.sansSerif{font-family: verdana,arial,helvetica,sans-serif; font-size: 16px;color: #000000;}
.heading {font-family: verdana,arial,helvetica,sans-serif;font-size: 18px;font-weight: bold;color: #003366;}
.subHeadingEoa {font-family: verdana,arial,helvetica,sans-serif;font-size: 15px;font-weight: bold;color: #000000;}
.subHeading {font-family: verdana,arial,helvetica,sans-serif;font-size: 16px;font-weight: bold;color: #003366;}
.sidebarText {font-family: verdana,arial,helvetica,sans-serif;font-size: 11px;color: #003366;}
.sidebarTextBold {font-family: verdana,arial,helvetica,sans-serif;font-size: 11px;font-weight: bold;color: #003366;}
.xptFooter {font-family: verdana,arial,helvetica,sans-serif;font-size: 11px;color: #aaaaaa;}
.button {font-size: 13px; font-family: verdana,arial,helvetica,sans-serif; font-weight: 400; border-style:outset; color:#000000; background-color: #cccccc;}
.smaller {font-family: verdana,arial,helvetica,sans-serif;font-size: 10px;color: #000000;}

Also danke erstmal für die Antwort, aber das problem konnte ich noch nicht lösen.
ich habe schon auf HTML-Mail in der Ansicht gestellt.
Welchen Klienten der Sender hat weiß ich nicht. Die Mails sind von Paypal.
Als Reintext steht genau dasselbe da.

Vll kann jemand was mit dem Quelltext anfangen:
From - Sun Apr 15 12:26:32 2007
X-Account-Key: account2
X-UIDL: 201009709
X-Mozilla-Status: 0001
X-Mozilla-Status2: 00000000
Received: from [216.113.188.96] (helo=outbound2.den.paypal.com)
by mx10.web.de with esmtp (WEB.DE 4.107 #114)
id 1HZT8G-0008Im-00
for xxxxxxxxxx; Thu, 05 Apr 2007 16:40:12 +0200
Received: from denweb137.den.paypal.com (denweb137.den.paypal.com [10.191.12.185])
by outbound2.den.paypal.com (8.13.7/8.13.8) with SMTP id l35EdiH3003755
for <xxxxxxxxxxxxxxxxxx>; Thu, 5 Apr 2007 07:39:44 -0700
X-DomainKeys: Sendmail DomainKeys Filter v0.4.1 outbound2.den.paypal.com l35EdiH3003755
DomainKey-Signature: a=rsa-sha1; s=dkim; d=paypal.de; c=nofws; q=dns;
b=R1YMd9dab+JwPyjldxGUln7qx/aSvFBJ6wJSbhjmQV0AsLutnujnCWN7GEiXW5vyn
g4ucx+5trmxeKtVL5+XaQCcf7GKIWmCLMQxH3kW/iyXhwNGYnfk+DRtTcotcM+eR6q5
PC8lEHTA5zI9jQxYAIgZ6KZwwPGMgpL1qvgveL8=
Received: (qmail 7346 invoked by uid 99); 5 Apr 2007 14:39:44 -0000
Date: Thu, 05 Apr 2007 07:39:44 -0700
Message-Id: xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Subject: =?windows-1252?Q?Ihre_PayPal-Zahlung_per_Bank=FCberweisung?=
X-MaxCode-Template: email_eft_new_payment
To: =?windows-1252?Q?Christian_Wei=DF?= <xxxxxxxxxxxxx>
From: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
X-Email-Type-Id: PP543
X-XPT-XSL-Name: /default/de_DE/account/EFTNewPayment.xsl
MIME-Version: 1.0
Sender: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
From: "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
To: xxxxxxxxxxxxxxxxxxxxxx
Subject: Ihre PayPal-Zahlung per Banküberweisung
Date: Thu, 05 Apr 2007 16:40:19 +0200
Content-Type: multipart/mixed; boundary="DORIS45CD56BD"

This is a MIME encoded message.
--DORIS45CD56BD
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: 8bit

<style type="text/css">BODY, TD {font-family: verdana,arial,helvetica,sans-serif;font-size: 12px;color: #000000;}