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 ----{
  "html_body": [],
  "text_body": [],
  "attachments": [],
  "parts": [
    {
      "headers_rfc": {
        "content_type": {
          "ContentType": {
            "c_type": "multipart",
            "c_subtype": "mixed",
            "attributes": {
              "boundary": ":foo"
            }
          }
        }
      },
      "headers_raw": [
        [
          {
            "Rfc": "content_type"
          },
          {
            "start": 13,
            "end": 47
          }
        ]
      ],
      "is_encoding_problem": false,
      "body": {
        "Multipart": []
      },
      "offset_header": 0,
      "offset_body": 48,
      "offset_end": 160
    }
  ]
}