Relays, aliases & traces
07Mail can pass through relays, gateways, aliases, and mailing lists before final delivery.
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
DIAGRAM§ 4.4 ↗
RFC 5321 · § 4.4EXAMPLE
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04
Leave diagnostic evidence.
Operators can inspect the chain when investigating delays and routing loops.
Protocol participantThreat or exceptionProtocol controlSimplified drawings · precise section references
Read the updated RFC section ↗
Preserve the trace while forwarding responsibly.
- An SMTP receiver adds a Received trace entry; existing trace entries are not reordered or rewritten by relays.
- Final delivery inserts Return-Path from the reverse-path under the defined rules.
- Aliases and mailing lists differ in responsibility and envelope handling; gateways bridge transport environments.
Received entries help diagnose loops, but can disclose topology. Implementations need loop-detection controls and must not expose blind-copy recipient sets through trace data.
Read the RFC section ↗Diagrams simplify the RFC. Read the linked sections for complete requirements.
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