/ENCODING_TYPE=encoding-type

    Overrides the default Content-Transfer-Encoding and sets it to the
    specified type.  Permissible types are:  7Bit, 8Bit, Base64, or
    Quoted-Printable.

    Experimentation may be necessary to achieve the desired result.
    However, it is suggested to use Base64 for most binary files,
    such as JPG and GIF image files.