Subject: RFC 8621 Section 4.1.4 test
Content-Type: multipart/mixed; boundary="1"

--1
Content-Type: text/plain
Content-Disposition: inline

A
--1  
Content-Type: multipart/mixed; boundary="2"

--2
Content-Type: multipart/alternative; boundary="3"

--3
Content-Type: multipart/mixed; boundary="4"

--4
Content-Type: text/plain
Content-Disposition: inline

B
--4  
Content-Type: image/jpeg
Content-Disposition: inline

C
--4  
Content-Type: text/plain
Content-Disposition: inline

D
--4--

--3 
Content-Type: multipart/related; boundary="5"

--5
Content-Type: text/html

<html>E</html>
--5  
Content-Type: image/jpeg

F
--5--  

--3-- 

--2   
Content-Type: image/jpeg
Content-Disposition: attachment

G
--2  
Content-Type: application/x-excel

H
--2  
Content-Type: message/rfc822

Subject: J

J
--2--

--1  
Content-Type: text/plain
Content-Disposition: inline

K
--1--

---- EXPECTED STRUCTURE ----
{
  "header": {
    "subject": "RFC 8621 Section 4.1.4 test",
    "content_type": {
      "c_type": "multipart",
      "c_subtype": "mixed",
      "attributes": {
        "boundary": "1"
      }
    }
  },
  "html_body": [
    {
      "contents": "<html><body>A</body></html>"
    },
    {
      "header": {
        "content_type": {
          "c_type": "text",
          "c_subtype": "html"
        }
      },
      "contents": "<html>E</html>"
    },
    {
      "contents": "<html><body>K</body></html>"
    }
  ],
  "text_body": [
    {
      "header": {
        "content_disposition": {
          "c_type": "inline"
        },
        "content_type": {
          "c_type": "text",
          "c_subtype": "plain"
        }
      },
      "contents": "A"
    },
    {
      "header": {
        "content_disposition": {
          "c_type": "inline"
        },
        "content_type": {
          "c_type": "text",
          "c_subtype": "plain"
        }
      },
      "contents": "B"
    },
    0,
    {
      "header": {
        "content_disposition": {
          "c_type": "inline"
        },
        "content_type": {
          "c_type": "text",
          "c_subtype": "plain"
        }
      },
      "contents": "D"
    },
    {
      "header": {
        "content_disposition": {
          "c_type": "inline"
        },
        "content_type": {
          "c_type": "text",
          "c_subtype": "plain"
        }
      },
      "contents": "K"
    }
  ],
  "attachments": [
    {
      "InlineBinary": {
        "header": {
          "content_disposition": {
            "c_type": "inline"
          },
          "content_type": {
            "c_type": "image",
            "c_subtype": "jpeg"
          }
        },
        "contents": [
          67
        ]
      }
    },
    {
      "Binary": {
        "header": {
          "content_type": {
            "c_type": "image",
            "c_subtype": "jpeg"
          }
        },
        "contents": [
          70
        ]
      }
    },
    {
      "Binary": {
        "header": {
          "content_disposition": {
            "c_type": "attachment"
          },
          "content_type": {
            "c_type": "image",
            "c_subtype": "jpeg"
          }
        },
        "contents": [
          71
        ]
      }
    },
    {
      "Binary": {
        "header": {
          "content_type": {
            "c_type": "application",
            "c_subtype": "x-excel"
          }
        },
        "contents": [
          72
        ]
      }
    },
    {
      "Message": {
        "header": {
          "subject": "J"
        },
        "html_body": [
          {
            "contents": "<html><body>J</body></html>"
          }
        ],
        "text_body": [
          {
            "contents": "J"
          }
        ]
      }
    }
  ]
}