Keep references, payloads and trust separate
05These schemes address messages and body parts. They neither authenticate the author nor guarantee that referenced data is available or safe to process.
After selecting an image part by ID, a MIME reader may separately decode a declared base64 payload. Percent decoding the cid URL and interpreting the part body are different operations; neither operation alone validates image safety.
Source for this drawing: RFC 2392 · Read RFC section 3 ↗
New to this? Start hereA quick picture + helpful background
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.
Identifier values can reveal the same environmental clues as the corresponding Message-ID or Content-ID headers. RFC 2392 calls for precautions when that disclosure could expose confidential information.
- Identifier values can reveal the same environmental clues as the corresponding Message-ID or Content-ID headers. RFC 2392 calls for precautions when that disclosure could expose confidential information.
- A cid or mid reference is not a signature, encryption mechanism or grant of access. Message handling, authorization and content-safety policy remain separate from identifier conversion.
- If the selected scope has no matching part, the teaching lookup reports missing data. It does not reinterpret the identifier’s suffix as an HTTP host or an email recipient.
- URL percent encoding applies to the identifier. A body part’s Content-Transfer-Encoding, such as base64, separately describes its payload representation under MIME; resolving the ID does not decode or validate the body.
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 ↗