Content-Type: multipart/mixed; boundary=":foo"

--:foo
--:foo
Content-Type: text/plain
--:foo
Content-Type: text/plain
--:foo
Content-Type: text/html
--:foo--

---- EXPECTED STRUCTURE ----
{
  "headers": {
    "values": {
      "content_type": {
        "ContentType": {
          "c_type": "multipart",
          "c_subtype": "mixed",
          "attributes": {
            "boundary": ":foo"
          }
        }
      }
    },
    "offsets": [
      {
        "name": {
          "Rfc": "content_type"
        },
        "start": 13,
        "end": 47
      }
    ]
  },
  "structure": {
    "List": []
  },
  "offset_header": 0,
  "offset_body": 48,
  "offset_end": 160
}