yf_mail_driver_internal class

    public function send(array $params = [], &$error_message = '')
    {
        $CRLF = "\r\n";
        $TAB = "\t";

        $params['charset'] = ($params['charset'] ?? null) ?: conf('charset') ?: $this->PARENT->DEFAULT_CHARSET ?: 'utf-8';
        $params['mailer_name'] = ($params['mailer_name'] ?? null) ?: $this->PARENT->DEFAULT_MAILER_NAME;
        $params['text'] = ($params['text'] ?? null) ?: 'Sorry, but you need an html mailer to read this mail.';

        $OB = '----=_OuterBoundary_000';
        $IB = '----=_InnerBoundery_001';

        $headers = 'MIME-Version: 1.0' . $CRLF;
        $headers .= $params['email_from'] ? 'From:' . $params['name_from'] . '<' . $params['email_from'] . '>' . $CRLF : '';
        $headers .= $params['email_to'] ? 'To:' . $params['name_to'] . '<' . $params['email_to'] . '>' . $CRLF : '';
        $headers .= $params['email_from'] ? 'Reply-To:' . $params['name_from'] . '<' . $params['email_from'] . '>' . $CRLF : '';

        $params['priority'] && $headers .= 'X-Priority:' . (int) ($params['priority']) . $CRLF;
        $headers .= 'X-Mailer:' . $params['mailer_name'] . $CRLF;
        $headers .= 'Content-Type:multipart/mixed;' . $CRLF . $TAB . 'boundary="' . $OB . '"' . $CRLF;
        // Messages start with text/html alternatives in OB
        $msg = 'This is a multi-part message in MIME format.' . $CRLF;
        $msg .= $CRLF . '--' . $OB . $CRLF;
        if (strlen($params['text']) || strlen($params['html'])) {
            $msg .= 'Content-Type: multipart/alternative;' . $CRLF . $TAB . 'boundary="' . $IB . '"' . $CRLF . $CRLF;
        }
        // plaintext section
        if (strlen($params['text'])) {
            $msg .= $CRLF . '--' . $IB . $CRLF;
            $msg .= 'Content-Type: text/plain;' . $CRLF . $TAB . 'charset="' . $params['charset'] . '"' . $CRLF;
            $msg .= 'Content-Transfer-Encoding: quoted-printable' . $CRLF . $CRLF;
            // plaintext goes here
            $msg .= $params['text'] . $CRLF . $CRLF;
        }
        // html section
        if (strlen($params['html'])) {
            $msg .= $CRLF . '--' . $IB . $CRLF;
            $msg .= 'Content-Type: text/html;' . $CRLF . $TAB . 'charset="' . $params['charset'] . '"' . $CRLF;
            $msg .= 'Content-Transfer-Encoding: base64' . $CRLF . $CRLF;
            // html goes here
            $msg .= chunk_split(base64_encode($params['html'])) . $CRLF . $CRLF;
        }
        // end of IB
        if (strlen($params['text']) || strlen($params['html'])) {
            $msg .= $CRLF . '--' . $IB . '--' . $CRLF;
        }
        // attachments
        if ($this->ALLOW_ATTACHMENTS) {
            foreach ((array) $params['attaches'] as $att_file) {
                $file_name = basename($att_file);
                $msg .= $CRLF . '--' . $OB . $CRLF;
                $msg .= 'Content-Type: application/octetstream;' . $CRLF . $TAB . 'name="' . $file_name . '"' . $CRLF;
                $msg .= 'Content-Transfer-Encoding: base64' . $CRLF;
                $msg .= 'Content-Disposition: attachment;' . $CRLF . $TAB . 'filename="' . $file_name . '"' . $CRLF . $CRLF;
                // file goes here
                $msg .= chunk_split(base64_encode(@file_get_contents($att_file)));
                $msg .= $CRLF . $CRLF;
            }
        }
        // message ends
        $msg .= $CRLF . '--' . $OB . '--' . $CRLF;
        // Send composed email
        return mail(
            $params['email_to'],
            $params['subject'],
            $msg,
            $headers,
            implode('', $params['mta_params'])
        );
    }

    public function __call($name, $args)
    {
        return main()->extend_call($this, $name, $args);
    }

    public function _init()
    {
        $this->PARENT = _class('send_mail');
    }