Parse multipart boundaries before interpreting nested MIME media types

Use this document to resolve one bounded operational decision: Parse multipart boundaries before interpreting nested MIME media types. Only the official source and traced locations below supply facts. Confirm applicability before acting.

Source fact:

The official RFC 2046 — Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types from RFC Editor / Internet Engineering Task Force supports the following bounded statements:

• A multipart body is divided by boundary lines into parts, each containing its own content headers, a blank line, and a body. The research record locates this support at Section 5.1 (Multipart Media Type).
• The multipart Content-Type requires a boundary parameter, and the chosen delimiter must not occur as a delimiter line inside any encapsulated part. The research record locates this support at Section 5.1.1 (Common Syntax).
• While parsing a nested multipart, a MIME implementation must recognize an outer boundary at every inner nesting level, including when an inner entity is truncated. The research record locates this support at Section 5.1.2 (Handling Nested Messages and Multiparts).

Do not import neighboring assumptions into the source record. The supported task is a scoped comparison involving sending domains, receiving domains, message agents, headers, authentication results, policy records, and failure handling and the conditions the source actually describes.

What the source does not establish

This RFC evidence supports only the named mail-protocol decision; it does not prove provider support, deliverability, or compliance for a particular flow. The citation is not a substitute for observed state, authorization, compliance evidence, or dependency health. Examine authoritative DNS, certificates, time, gateways, identity stores, reputation services, and third-party mail providers before translating the source into an operational decision.

Applicability questions

• For source statement 1 at Section 5.1 (Multipart Media Type), which observable configuration, record, or test can confirm applicability here?
• For source statement 2 at Section 5.1.1 (Common Syntax), which observable configuration, record, or test can confirm applicability here?
• For source statement 3 at Section 5.1.2 (Handling Nested Messages and Multiparts), which observable configuration, record, or test can confirm applicability here?
• Within sending domains, receiving domains, message agents, headers, authentication results, policy records, and failure handling, which versions, roles, and configuration states define the review population?
• Could authoritative DNS, certificates, time, gateways, identity stores, reputation services, and third-party mail providers invalidate the test, hide a failure, or change applicability?
• Who owns the decision, and which observation requires stopping, escalation, or rollback?

DSE recommendation:

DSE recommends using the cited source as the evidence anchor for this decision. Use a two-person review for the source interpretation and the resulting operational decision. Record the source location, examined part of sending domains, receiving domains, message agents, headers, authentication results, policy records, and failure handling, observed and expected states, owner, and reason for deviation.

Translate the conclusion into change control only after documenting dependencies, impact, test method, expected signals, failure signals, and restoration steps. Include authoritative DNS, certificates, time, gateways, identity stores, reputation services, and third-party mail providers, while excluding secrets and sensitive personal or topology data from ordinary tickets.

Verification and evidence

Tie each conclusion back to Section 5.1 (Multipart Media Type); Section 5.1.1 (Common Syntax); Section 5.1.2 (Handling Nested Messages and Multiparts) and to observable material such as sanitized messages, DNS records, SMTP transcripts, authentication results, policy evaluation, and delivery or rejection logs. Preserve provenance and stable identifiers without copying secrets into the evidence set.

Retain the starting state, authorization, execution record, outcome, deviation, and final state as one review package. Move disruptive checks to an approved test path. Reopen the decision when versions, design, dependencies, ownership, or official guidance changes.

Official references

• RFC 2046 — Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types — RFC Editor / Internet Engineering Task Force