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RFC 2047 / EMAIL ENCODED WORDS

Read the encoded-word wrapper

01

An encoded word packages a character set, a byte encoding and text into printable ASCII. It lets a compatible mail reader display non-ASCII header text.

DIAGRAMRead RFC section 2 ↗
RFC 2047 · § 2EXAMPLE
4 / 4
Read the encoded-word wrapperFour views of a chosen Subject encoded word. A mail composer writes the ASCII wrapper =?UTF-8?Q?caf=C3=A9?=. The next view separates charset UTF-8, encoding Q and the encoded payload. Byte decoding yields 63 61 66 c3 a9; UTF-8 interpretation gives café. Lowercase charset and encoding names have the same meaning. The display assumes charset support and does not authenticate a sender.RFC2047 · header text in an ASCII wrapper=?utf-8?q?caf=C3=A9?=case-independent namesSame charset + same encodingSame display: caféDifferent charsets need not interpret bytes alike
04
Names may differ in case, not meaning.

The chosen =?utf-8?q?caf=C3=A9?= has the same interpretation. A reader must know the declared charset; case-insensitivity does not make arbitrary charsets interchangeable.

Source for this drawing: RFC 2047 · Read RFC section 2 ↗

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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 5322 Email message format RFC 2045 MIME message bodies RFC 3629 UTF-8

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Related RFCs and changes

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

KEY POINT

Keep the character set, encoding and payload together.

  • Keep the character set, encoding and payload together.
  • The base form is =?charset?encoding?encoded-text?=. Charset and encoding names are case-insensitive. No unencoded white space may appear inside the word; the payload cannot contain a literal question mark.
  • Q and B are the defined encodings. A conforming reader MUST accept both for every character set it supports; declaring a charset does not guarantee every reader supports it.
DETAILS

Chosen examples assume a reader that supports UTF-8, a Unicode byte encoding. MIME means Multipurpose Internet Mail Extensions; ASCII is the seven-bit interchange character set. This is header text, not a body Content-Transfer-Encoding or authentication mechanism. Registered charset names identify the byte-to-character interpretation; a UTF-8 byte sequence is not the same as Latin-1. The old §3 ISO-8859 preference is historical advice, not a rule to replace Unicode today. Verified erratum506 restores the backslash excluded from token names. A MIME-Version header is not required for recognizing these words (§6.1).

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