rfc3391-2: The value of the "type" parameter must be the content-type of
the root message

rfc3391-3: An Application/Vnd.pwg-multiplexed entity contains a sequence of
chunks. Each chunk consists of a chunk header, a chunk payload and a CRLF.

rfc3391-4: The chunk header consists of a "CHK" keyword followed by the
message number, the chunk payload length, whether the chunk is the last
chunk of a message and, finally, a CRLF

rfc3391-5: The chunk payload is a sequence of octets that is either a
complete message or a part of a message.   

rfc3391-7: The first chunk contains a complete or partial message that (in
either case) represents the root component of the compound object.  

rfc3391-9: The final chunk's header contains a message number of 0, a
length of 0 and a last-chunk-of-message mark (i.e., the chunk header line
is "CHK 0 0 LAST").  

rfc3391-17: The type parameter must be specified.  Its value is the
 content-type of the "root" message.