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RFC 2047 / EMAIL ENCODED WORDS

Split long text at complete character boundaries

04

A long header may use several encoded words, but each word must stand alone. Wrapper length, line length, byte escapes and character boundaries are separate checks.

DIAGRAMRead RFC section 2 ↗
RFC 2047 · § 2EXAMPLE
4 / 4
Split long text at complete character boundariesFour separate boundary checks. A UTF-8 Q wrapper has 12 characters of overhead; 63 plain ASCII payload characters make a 75-character word.64 would make 76 and stop at the word gate. A separate failed UTF-8 split puts c3 and a9 from one é character in different words. Folding between complete words keeps Subject on its own line and a leading space plus 75-character word at 76. The length bars are schematic, not literal wire words.Word, byte, character and line limitsLength schematic, not literal wire data:Subject: 8 charactersSP + [75-character word] 76 charactersSP + [75-character word] 76 charactersCRLF between complete wordsEach continuation starts with white spaceCheck the field name and leading space in line length
04
Fold between self-contained words.

A line holding Subject: plus a 75-character word would be too long. Put Subject: on its own line, then SP plus a 75-character word:76 characters. Each continuation word stands alone; display joining is the next chapter’s rule.

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

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KEY POINT

Each encoded word must be complete and at most 75 characters.

  • Each encoded word must be complete and at most 75 characters.
  • The 75-character limit includes charset, encoding, payload and delimiters. Lines containing encoded words are limited to 76 characters. Include the field name or continuation white space when checking a line.
  • Each word MUST encode integral octets and characters. Q =HH sequences and B groups cannot continue in another word; a multi-octet character MUST NOT be split. Fold between words using CRLF plus white space, never inside a word.
DETAILS

The limit drawing is a length schematic, not a literal long wire word. For the chosen UTF-8 Q wrapper, overhead is 12 characters: 63 plain A payload characters give 75;64 give 76 and do not fit. A longer charset or language tag changes the payload budget. UTF-8 é consists of c3 a9 and must stay in one word. The teaching splitter is limited to supported UTF-8/US-ASCII/Latin-1 examples; it is not a complete stateful-charset mail composer.

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