Horde_Mime_Part::_getTransferEncoding PHP Method

    protected function _getTransferEncoding($encode = self::ENCODE_7BIT)
    {
        if (!empty($this->_temp['sendEncoding'])) {
            return $this->_temp['sendEncoding'];
        } elseif (!empty($this->_temp['sendTransferEncoding'][$encode])) {
            return $this->_temp['sendTransferEncoding'][$encode];
        }
        if (empty($this->_contents)) {
            $encoding = '7bit';
        } else {
            switch ($this->getPrimaryType()) {
                case 'message':
                case 'multipart':
                    /* RFC 2046 [5.2.1] - message/rfc822 messages only allow 7bit,
                     * 8bit, and binary encodings. If the current encoding is
                     * either base64 or q-p, switch it to 8bit instead.
                     * RFC 2046 [5.2.2, 5.2.3, 5.2.4] - All other messages
                     * only allow 7bit encodings.
                     *
                     * TODO: What if message contains 8bit characters and we are
                     * in strict 7bit mode? Not sure there is anything we can do
                     * in that situation, especially for message/rfc822 parts.
                     *
                     * These encoding will be figured out later (via toString()).
                     * They are limited to 7bit, 8bit, and binary. Default to
                     * '7bit' per RFCs. */
                    $default_8bit = 'base64';
                    $encoding = '7bit';
                    break;
                case 'text':
                    $default_8bit = 'quoted-printable';
                    $encoding = '7bit';
                    break;
                default:
                    $default_8bit = 'base64';
                    /* If transfer encoding has changed from the default, use that
                     * value. */
                    $encoding = $this->_transferEncoding == self::DEFAULT_ENCODING ? 'base64' : $this->_transferEncoding;
                    break;
            }
            switch ($encoding) {
                case 'base64':
                case 'binary':
                    break;
                default:
                    $encoding = $this->_scanStream($this->_contents);
                    break;
            }
            switch ($encoding) {
                case 'base64':
                case 'binary':
                    /* If the text is longer than 998 characters between
                     * linebreaks, use quoted-printable encoding to ensure the
                     * text will not be chopped (i.e. by sendmail if being
                     * sent as mail text). */
                    $encoding = $default_8bit;
                    break;
                case '8bit':
                    $encoding = $encode & self::ENCODE_8BIT || $encode & self::ENCODE_BINARY ? '8bit' : $default_8bit;
                    break;
            }
        }
        $this->_temp['sendTransferEncoding'][$encode] = $encoding;
        return $encoding;
    }