("multipart/mixed" 0
 ("text/plain" 0
  "  ...Introductory text or table of contents...\n")
 ("multipart/digest" 1
  ("message/rfc822" 0
   ("text/plain" 0
    "  ...body goes here ...\n"))
  ("message/rfc822" 1
   ("text/plain" 0
    "  ... another body goes here ...\n"))
 )
)
