To: list@example.com
From: user@example.com
Subject: Test multipart with null byte in body.
Message-ID:  <0307537c-35d6-6f67-597c-2181ac67beef@example.com>
Date: Fri, 12 Mar 2021 11:22:55 -0800
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="aaaa"

--aaaa
Content-Type: text/plain; charset="us-ascii"

The body with a -> <- null byte
--aaaa
Content-Type: application/octet-stream

The attachment with a -> <- null byte
--aaaa
Content-Type: text/plain; charset="us-ascii"

-- 
A sig with a -> <- null byte
--aaaa--
