To: test@example.com
From: test@example.com
Subject: 6 plaintext + HMTL
Message-ID: <a30f750d-d56c-8a52-971c-f95a131e8332@example.com>
Date: Sat, 30 Dec 2017 19:31:21 +0100
User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:59.0) Gecko/20100101
 Thunderbird/59.0a1
MIME-Version: 1.0
Content-Type: multipart/alternative;
 boundary="------------FAB286B8794CC63C0A0FD1BB"
Content-Language: de-DE

This is a multi-part message in MIME format.
--------------FAB286B8794CC63C0A0FD1BB
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: base64

U2VhcmNoIGZvciBoaWhp


--------------FAB286B8794CC63C0A0FD1BB
Content-Type: text/html; charset=windows-1252
Content-Transfer-Encoding: base64

PGJvZHk+U2VhcmNoIGZvciA8Yj5odWh1PC9iPjwvYm9keT4=

--------------FAB286B8794CC63C0A0FD1BB--