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RFC 3848 / MAIL TRANSMISSION TRACE

Find the transport label in a Received field

01

ESMTP means Extended Simple Mail Transfer Protocol. A receiving server adds a Received trace field; its with clause names the transmission type used on that incoming hop.

DIAGRAMRead RFC section 1 ↗
RFC 3848 · § 1EXAMPLE
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Find the transport label in a Received fieldThree trace creation states. Sender sends a message to receiving relay. Receiver prepends its own Received excerpt naming source, receiver and with ESMTP; date and other fields are omitted. A later receiver adds its trace above the older field without rewriting it. Stacked fields run newest to oldest from top to bottom. The with token describes incoming transmission, not message author or every hop.Record the receiving hopNewer: from relay.exampleby next.example with ESMTPOlder: from sender.exampleby relay.example with ESMTPNext receiver prepends; older field staysRoute chronology: bottom → top
03
Add the next reception above it.

The next receiver prepends a newer field while retaining the earlier one below. Read the route chronologically from the older bottom entry toward the newer top entry.

Source for this drawing: RFC 3848 · Read RFC section 1 ↗

Protocol participantThreat or exceptionProtocol controlSimplified drawings · precise section references
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

RFC 5321 SMTP RFC 5322 Email message format RFC 3207 SMTP STARTTLS

These pictures are analogies to help you learn. The linked RFC explains the actual rules.

Related RFCs and changes

“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.

KEY POINT

A trace label describes one reception, not the whole message.

  • RFC 3848 registers seven additional WITH protocol types, not a new SMTP command or an EHLO capability.
  • RFC 5321 §4.4 requires receiving SMTP servers to prepend Received fields and forbids changing or reordering earlier Received lines.
  • Examples here show header excerpts only. Complete Received fields also contain other information and a date.
DETAILS

Existing SMTP and ESMTP labels predate these seven registrations.

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