defines mechanisms for sending other kinds of information in e-mail, including text in languages other than English, using character encodings other than ASCII. However, these encodings often use byte values outside the ASCII range so they need to be encoded further before they are suitable for use in a non-8-bit-clean environment. Quoted-Printable encoding is one method used for mapping arbitrary bytes into sequences of ASCII characters. So, Quoted-Printable is not a character encoding scheme itself, but a data coding layer to be used under some byte-orientedcharacter encoding. QP encoding is reversible, meaning the original bytes and hence the non-ASCII characters they represent can be identically recovered. Quoted-Printable and Base64 are the two basic MIME content transfer encodings, if a trivial "8bit" encoding is not counted. If the text to be encoded does not contain many non-ASCII characters, then Quoted-Printable results in a fairly readable and compact encoded result. On the other hand, if the input is not mostly ASCII, then Quoted-Printable becomes both unreadable and extremely inefficient. Base64 is not human-readable, but has a uniform overhead for all data and is the more sensible choice for binary formats or text in a script other than Latin script.
Quoted-Printable encoding
Any 8-bit byte value may be encoded with 3 characters: an = followed by two hexadecimal digits representing the byte's numeric value. For example, an ASCII form feed character can be represented by "=0C", and an ASCII equal sign must be represented by =3D. All characters except printable ASCII characters or end of line characters must be encoded in this fashion. All printable ASCII characters may be represented by themselves, except =. ASCII tab and space characters, decimal values 9 and 32, may be represented by themselves, except if these characters would appear at the end of the encoded line. In that case, they would need to be escaped as =09 or =20, or be followed by a = as the last character of the encoded line. This last solution is valid because it prevents the tab or space from being the last character of the encoded line. If the data being encoded contains meaningful line breaks, they must be encoded as an ASCII CR LF sequence, not as their original byte values, neither directly nor via = signs. Conversely, if byte values 13 and 10 have meanings other than end of line, then they must be encoded as =0D and =0A respectively. Lines of Quoted-Printable encoded data must not be longer than 76 characters. To satisfy this requirement without altering the encoded text, soft line breaks may be added as desired. A soft line break consists of an = at the end of an encoded line, and does not appear as a linebreak in the decoded text. These soft line breaks also allow encoding text without line breaks for an environment where line size is limited, such as the 1000 characters per line limit of some SMTP software, as allowed by RFC 2821. A slightly modified version of Quoted-Printable is used in message headers; see MIME#Encoded-Word.
Example
The following example is a French text, with a high frequency of letters with diacritical marks. J'interdis aux marchands de vanter trop leurs marchandises. Car ils se font = vite p=C3=A9dagogues et t'enseignent comme but ce qui n'est par essence qu'= un moyen, et te trompant ainsi sur la route =C3=A0 suivre les voil=C3=A0 bi= ent=C3=B4t qui te d=C3=A9gradent, car si leur musique est vulgaire ils te f= abriquent pour te la vendre une =C3=A2me vulgaire. This encodes the following quotation:
