From: from@there.com
To: to@here.com
Subject: Test
Date: Fri, 29 Sep 2017 10:55:23 +0200
MIME-Version: 1.0
Content-Type: multipart/mixed;
 boundary="------------5B1F217006A67C28E756A62E"

This is a multi-part message in MIME format.
--------------5B1F217006A67C28E756A62E
Content-Type: text/plain; charset=iso-8859-15; format=flowed
Content-Transfer-Encoding: 7bit

Test

--------------5B1F217006A67C28E756A62E
Content-Type: text/plain; charset=UTF-8;
 name="MyFile.txt"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
 filename="MyFile.txt"

TXlGaWxlQ29udGVudA==
--------------5B1F217006A67C28E756A62E--