Negotiate SMTP STARTTLS without implying authenticated delivery

Treat this document as a focused evidence review: Negotiate SMTP STARTTLS without implying authenticated delivery. Only the official source and traced locations below supply facts. Confirm applicability before acting.

Source fact:

The official RFC 3207 — SMTP Service Extension for Secure SMTP over Transport Layer Security from RFC Editor supports the following bounded statements:

• After a 220 response to STARTTLS, the client begins the TLS handshake before sending any further SMTP command. The research record locates this support at Section 4 (The STARTTLS Command).
• A successful TLS handshake resets SMTP to its initial state; both peers discard pre-TLS protocol knowledge and the client sends a new EHLO. The research record locates this support at Section 4.2 (Result of the STARTTLS Command).
• A public MX on port 25 cannot require STARTTLS for local delivery, although relay policy may depend on authentication obtained during TLS. The research record locates this support at Section 4 (The STARTTLS Command), public-server rule.

The source support ends with the statements listed above. Use them to examine sending domains, receiving domains, message agents, headers, authentication results, policy records, and failure handling in the applicable environment, not to imply a wider guarantee.

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 4 (The STARTTLS Command), which observable configuration, record, or test can confirm applicability here?
• For source statement 2 at Section 4.2 (Result of the STARTTLS Command), which observable configuration, record, or test can confirm applicability here?
• For source statement 3 at Section 4 (The STARTTLS Command), public-server rule, 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. Make the source, asset scope, owner, and expected outcome explicit in the review record. 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.

An implementation decision needs an owner, approved window, prechecks, observable outcome, stop authority, and rollback path. Validate authoritative DNS, certificates, time, gateways, identity stores, reputation services, and third-party mail providers before and after the test, and store only sanitized operational evidence.

Verification and evidence

A reviewer should be able to retrace the decision from Section 4 (The STARTTLS Command); Section 4.2 (Result of the STARTTLS Command); Section 4 (The STARTTLS Command), public-server rule through sanitized messages, DNS records, SMTP transcripts, authentication results, policy evaluation, and delivery or rejection logs. Record what was collected, where, when, by whom, and which system or role it represents.

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 3207 — SMTP Service Extension for Secure SMTP over Transport Layer Security — RFC Editor