What is the Email Content-Type Header (ie MIME)?

About

Content-type is a email headers that defines:

• the type of the body
• or the type of one of the body parts

Example

Where the first parameter is the media type (mime)

Single part

• HTML

Content-Type: text/html; charset="UTF-8"

• Plain Text

Content-Type: text/plain; charset="UTF-8"

• A content that is a mime message (ie rfc822). ie a mail inside a mail

Content-Type: message/rfc822

• Delivery Status

Content-Type: message/delivery-status

• Attached Image

Content-Type: image/png; name="icon.png"
Content-Disposition: attachment; filename="icon.png"
Content-Transfer-Encoding: base64
Content-ID: <icon.png>

Multipart

Multipart media type means that the body is composed of multiple single part

• Multipart alternative. The parts are alternative to each other and represent the same content. The client can show one or the other part. Normally used to show a text if the client does not support HTML rendering.

Content-Type: multipart/alternative; boundary="0000000000008c12850607c40b30"

• Multipart related. The parts are related but do not represent the same content.

Content-Type: multipart/related; boundary="0000000000008c12780607c40b2f"

• Multipart report (in case of a bounce)

Content-Type: multipart/report; boundary="0000000000008c07b00607c40b27"; report-type=delivery-status

Syntax

It has the same functionality and syntax than the HTTP content type header

Namely:

Content-Type: mediaType; parameter1=value1; parameter2=value2

where:

• mediaType is the media type or mime
• parameters are extra information for the type