Format: ADD filename

    When editing a message draft or new message, this command attaches
    the specified file to the current message.  MIME maintains a list of
    known file types associated with various file name extensions; for
    example, files that end in ".TXT" are treated as text. Use the
    SHOW FILE_TYPES command to display this list of file types. To
    override the default file type associated with any file, use one
    of the ADD command qualifiers.