Return-Path: sender@domain.tld
From: Ye Olde Sender <sender@domain.tld>
Subject: =?UTF-8?Q?Message_=c3=a0_urlizer?=
To: my list <test@lists.example.com>
Message-ID: <deep-nested@domain.tld>
Date: Thu, 19 Dec 2019 11:03:19 +0100
MIME-Version: 1.0
Content-type: multipart/mixed; boundary="________boundary-level1"

This is a multi-part attachment message with deeply nested multipart sub-parts.

--________boundary-level1
Content-Type: multipart/alternative;
	boundary="________boundary-level2"

--________boundary-level2
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain;
	charset=utf-8

A simple text part. It is alternative with a multipart/mixed part.

--________boundary-level2
Content-Type: multipart/mixed;
	boundary="________boundary-level3"


--________boundary-level3
Content-Transfer-Encoding: quoted-printable
Content-Type: text/html;
	charset=utf-8

<html>
  <head></head>
  <body>A simple HTML part. It is alongside with a text attachment and a
   multipart/alternative that should both be urlized.</body>
</html>

--________boundary-level3
Content-Disposition: attachment;
	filename="=?UTF-8?Q?W=c3=bcrzburg=2etxt?="
Content-Type: text/plain;
	name="=?UTF-8?Q?W=c3=bcrzburg=2etxt?="
    charset=us-ascii
Content-Transfer-Encoding: 8bit

This is a text file attached to the message. It should be urlized.

--________boundary-level3
Content-Type: multipart/alternative;
	boundary="________boundary-level4"

--________boundary-level4
Content-Type: multipart/alternative;
	boundary="________boundary-level5"

--________boundary-level5
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain;
	charset=utf-8

A simple text part. The whole multipart/alternative part should be urlized.

--________boundary-level5
Content-Type: multipart/mixed;
	boundary="________boundary-level6"

--________boundary-level6
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain;
	charset=utf-8

A simple text part. 

--________boundary-level6
Content-Type: application/png;
 name="image.png"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
 filename="image.png"

JVBERi0xLjQNJeLjz9MNCjUgMCBvYmoNPDwvTGluZWFyaXplZCAxL0wgMTIzNzgxNi9PIDcv

--________boundary-level6--

--________boundary-level5--

--________boundary-level4--

--________boundary-level3--

--________boundary-level2--

--________boundary-level1--

