UTF-7

UTF-7 (7-bit Unicode Transformation Format) is a variable-length character encoding that is used to represent Unicode-encoded text using a stream of ASCII character for use in MIME messages.

MIME technically requires that the encoding used to send email is ASCII, so any email that uses a Unicode encoding is invalid. However, this restriction is universally ignored. UTF-7 allows mail to use Unicode but also follow the standards.

Description

UTF-7 is standardized as RFC 1642, A Mail-Safe Transformation Format of Unicode.

Characters below 128 within the ASCII range are encoded as is. Any character that falls outside that range are encoded with an escape sequence of a '+' character followed by the Unicode character code encoded in Base64, and terminated with a '-' character. Literal '+' characters are encoded with a '+-' sequence.

Examples

• "Hello, World!" is encoded as "Hello, World!"
• "1 + 1 = 2" is encoded as "1 +- 1 = 2"
• "A pint costs £1 today" is encoded as "A pint costs +ow-1 today"