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RFC 6152 / SMTP 8-BIT MIME TRANSPORT

Negotiate before sending an 8-bit body

01

SMTP transfers mail between a sending client and a receiving server. EHLO discovers whether this particular connection supports 8BITMIME.

DIAGRAMRead RFC section 3 ↗
RFC 6152 · § 3EXAMPLE
5 / 5
Negotiate before sending an 8-bit bodyFive moments of one fictional successful SMTP transfer, after the greeting. Client EHLO obtains a2508BITMIME capability with no parameter; MAIL FROM a at example com requests BODY equals8BITMIME once after the address. After MAIL250, RCPT b at example com gets250, then DATA gets354. The MIME body and dot terminator follow, then final250. A final acceptance is not proof of eventual delivery; unrelated extensions and ordinary error paths are omitted.Negotiate this connection, then this bodySMTP clientSMTP serverMIME content + dot terminatorChosen body text: café[CRLF]250 after DATAAll body bits preservedAccepted here ≠ proof of final delivery
05
Transfer, then read the result.

The chosen MIME body is transferred with its bits preserved and the dot terminator ends DATA. This example receives final 250; acceptance is not proof of final delivery.

Source for this drawing: RFC 6152 · Read RFC section 3 ↗

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.

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RFC 5321 SMTP RFC 2045 MIME message bodies RFC 3629 UTF-8

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KEY POINT

Negotiate the transport before sending high-bit body octets.

  • A successful EHLO reply must advertise 8BITMIME before this extension is used. The EHLO keyword has no parameter.
  • The extended MAIL command carries one BODY parameter after the envelope address, with value 7BIT or 8BITMIME. No new SMTP verb is defined.
  • RCPT chooses envelope recipients. DATA and a 354 reply still precede the body; final acceptance is distinct from eventual delivery.
DETAILS

The fictional dialogue omits the greeting and unrelated extensions. One successful path is shown; ordinary SMTP failures remain possible. SMTP means Simple Mail Transfer Protocol; MIME means Multipurpose Internet Mail Extensions.

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