Quotedprintable

Quoted-printable is a content-transfer-encoding used in MIME to transmit data over 7-bit channels such as SMTP. It is designed for text that is mostly ASCII, allowing non-ASCII characters to be included while keeping the data readable in its encoded form. It is defined by the MIME specifications in RFC 2045 and RFC 2046.

The encoding preserves most printable ASCII characters by transmitting them literally, with the exception of the equals sign, which must be represented as =3D. Any octet outside the ASCII printable range, or any non-ASCII byte, is encoded as = followed by two hexadecimal digits. Spaces and horizontal tabs at line ends must be encoded as =20 and =09, respectively. Lines are typically wrapped to a maximum of 76 characters, using a soft line break indicated by an equals sign at the end of a line to show continuation.

Quoted-printable is mainly used for textual data that is mostly ASCII but may include a few non-ASCII characters. It is not a compression scheme and can inflate the size of data containing many non-ASCII characters, especially when the underlying text uses UTF-8. For binary data, base64 is often more efficient. The exact encoded form depends on the character encoding of the source text; for example, an é may appear as =E9 in ISO-8859-1 or =C3=A9 in UTF-8.

See also MIME, RFC 2045, RFC 2046, and content-transfer-encoding.