Quoted-printable
The Quoted-Printable encoding is an escape syntax that uses printable ASCII characters (alphanumeric and the equals sign =) to represent arbitrary binary data to enable transmission of 8-bit data over a 7-bit data path or, generally, over a medium which is not 8-bit clean. Historically, because of the wide range of systems and protocols that could be used to transfer messages, e-mail was often assumed to be non-8-bit-clean – however, modern SMTP servers are in most cases 8-bit clean and support the 8BITMIME extension.