Reference an embedded MIME body part
01MIME means Multipurpose Internet Mail Extensions. It lets a message contain several body parts, each with its own headers and content. A cid URL lets one part refer to another.
The chosen boundary is picnic-boundary. Its delimiter is --picnic-boundary, followed directly by Content-ID and Content-Type headers. A blank line then starts the omitted image body. The example is a fragment, not a complete message.
Source for this drawing: RFC 2392 · Read RFC section 1 ↗
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A message needs an address.
Think of a packet as a small addressed envelope. Devices pass it onward; transport protocols decide what delivery promises an application gets.
Helpful first, if these ideas are unfamiliar
These pictures are analogies to help you learn. The linked RFC explains the actual rules.
Terms in this drawing
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
Content-ID identifies a MIME entity. Its header field value uses angle brackets, while the cid URL carries a URL-encoded identifier without those outer brackets.
- Content-ID identifies a MIME entity. Its header field value uses angle brackets, while the cid URL carries a URL-encoded identifier without those outer brackets.
- In the illustrated multipart/related message, an HTML part refers to an image part by Content-ID. The identifier’s domain-like suffix is not an instruction to fetch an HTTP image.
- RFC 2387 supplies the companion multipart/related rules. Our example specifies type="text/html" and uses the first part as its root; a start parameter could identify a different root.
- In this header-bearing example, the delimiter is followed immediately by the part headers. A blank line follows the header area and precedes the body; MIME also permits an empty header area. Verified erratum 6176 corrects the example.
Fictional .example identifiers; payloads are omitted. Consult the linked MIME and message-format specifications for complete parsing, retrieval and security requirements.
Read the RFC section ↗