Binary files cannot be transmitted directly as electronic mail;
    they must first be encoded into a "printable" format. This,
    of course, means that they must be decoded upon receipt. The
    ENCODING command is used to specify the encoding to be applied
    to files requested with the SEND command. When selecting an
    encoding, be sure to select an encoding which you can decode.
    If your mail is handled by PMDF, then you can decode any of the
    encodings offered by PMDF mail servers.

    The encoding specified with the ENCODING command applies to
    all subsequent SEND commands in the same message. It can be
    overridden with a subsequent ENCODING command or, on a per
    command, basis with the SEND command's /ENCODING qualifier. And,
    of course, encodings established in previous messages sent to
    the server have no effect on subsequent messages which you might
    send.

    The BASE64 and QUOTED_PRINTABLE encodings are described in RFC
    2045 (MIME, Part One). The HEXADECIMAL encoding is a simple
    hexadecimal encoding of the data. The data is encoded in 8 bit
    byte order. Each 8 bit byte is represented with two characters;
    the first character describes the high four bits and the second
    describes the low four bits. The UUENCODE encoding is compatible
    with the popular UUENCODE and UUDECODE utilities.

    BASE64 is usually the best encoding to use: it is most likely
    to survive any mangling that might occur as the mail message
    works its way through the networks to you (e.g., line wrapping,
    character set translation, space stripping, etc.).