subject: primary subject
content-type : multipart/(co\m\)ment)mumble mumble; boundary = "ab\cd 
 ef" mumble

abcdef prolog

--abcd ef
content-type: message/rfc822; mumble

subject: nested subject
content-type: multipart/mumble; boundary(comment)="pqrs"
content-transfer-encoding: base64

pqrs prolog

--pqrs
header: pqrs part 01

body pqrs part 01

--pqrs
header: pqrs part 02

body pqrs part 02

--bogus-boundary
header: wietse

body asdasads

--abcd ef
header: abcdef part 02

body abcdef part 02

--abcd ef--

epilog