Content-Type: multipart/mixed; boundary="1"
MIME-Version: 1.0

--1
Content-Type: text/plain

hello, world
--1
Content-Type: multipart/mixed; boundary="1"
MIME-Version: 2.0

--1
Content-Type: text/plain

hello, world
--1
Content-Type: multipart/mixed; boundary="1"
MIME-Version: abc

--1
Content-Type: text/plain

hello, world
--1
Content-Type: multipart/mixed; boundary="1"
MIME-Version:

--1
Content-Type: text/plain

hello, world
--1

---- EXPECTED STRUCTURE ----
{
  "header": {
    "mime_version": "1.0",
    "content_type": {
      "c_type": "multipart",
      "c_subtype": "mixed",
      "attributes": {
        "boundary": "1"
      }
    }
  },
  "html_body": [
    {
      "contents": "<html><body>hello, world</body></html>"
    },
    {
      "contents": "<html><body>hello, world</body></html>"
    },
    {
      "contents": "<html><body>hello, world</body></html>"
    },
    {
      "contents": "<html><body>hello, world</body></html>"
    }
  ],
  "text_body": [
    {
      "header": {
        "content_type": {
          "c_type": "text",
          "c_subtype": "plain"
        }
      },
      "contents": "hello, world"
    },
    {
      "header": {
        "content_type": {
          "c_type": "text",
          "c_subtype": "plain"
        }
      },
      "contents": "hello, world"
    },
    {
      "header": {
        "content_type": {
          "c_type": "text",
          "c_subtype": "plain"
        }
      },
      "contents": "hello, world"
    },
    {
      "header": {
        "content_type": {
          "c_type": "text",
          "c_subtype": "plain"
        }
      },
      "contents": "hello, world"
    }
  ]
}