Content-Type: multipart/mixed; boundary="1"
MIME-Version: 1.0

--1
Content-Type: text/plain

hello, world
--1
Content-Type: multipart/mixed; boundary="1"
MIME-Version: 2.0

--1
Content-Type: text/plain

hello, world
--1
Content-Type: multipart/mixed; boundary="1"
MIME-Version: abc

--1
Content-Type: text/plain

hello, world
--1
Content-Type: multipart/mixed; boundary="1"
MIME-Version:

--1
Content-Type: text/plain

hello, world
--1

