PHP supports sending classes for sending HTML format emails

        /**
 * Email sending class
 * Supports sending plain text emails and HTML format emails
 * @example
 * $config = array(
 * "from" => "*****",
 * "to" = > "***",
 * "subject" => "test",
 * "body" => "test",
 * "username" => "* **",
 * "password" => "****",
 * "isHTML" => true
 * );
 *
 * $mail = new MySendMail();
 *
 * $mail ->setServer("smtp.126.com");
 *
 * $mail->setMailInfo($config);
 * if(!$mail->sendMail()) {
 * echo $mail- >error();
 * return 1;
 * }
*/
    class MySendMail{
        /**
 * @var Mail transfer agent username
 * @access private
*/
        private $_userName;

        /**
 * @var Mail transfer agent password
 * @access private
*/
        private $_password;

        /**
 * @var Mail transfer proxy server address
 * @access protected
*/
        protected $_sendServer;

        /**
 * @var Mail transfer proxy server port
 * @access protected
*/
        protected $_port=25;

        /**
 * @var sender
 * @access protected
*/
        protected $_from;

        /**
 * @var recipient
 * @access protected
*/
        protected $_to;

        /**
 * @var theme
 * @access protected
*/
        protected $_subject;

        /**
 * @var Email text
 * @access protected
*/
        protected $_body;

        /**
 * @var Whether it is an email in HTML format
 * @access protected
*/
        protected $_isHTML=true;

        /**
 * @var socket resource
 * @access protected
*/
        protected $_socket;

        /**
 * @var error message
 * @access protected
*/
        protected $_errorMessage;

        public function __construct($from="", $to="", $subject="", $body="", $server="", $username="", $password="",$isHTML="", $port="") {
            if(!empty($from)){
                $this->_from = $from;
            }
            if(!empty($to)){
                $this->_to = $to;
            }
            if(!empty($subject)){
                $this->_subject = $subject;
            }
            if(!empty($body)){
                $this->_body = $body;
            }
            if(!empty($isHTML)){
                $this->_isHTML = $isHTML;
            }
            if(!empty($server)){
                $this->_sendServer = $server;
            }
            if(!empty($port)){
                $this->_port = $port;
            }
            if(!empty($username)){
                $this->_userName = $username;
            }
            if(!empty($password)){
                $this->_password = $password;
            }
        }

        /**
 * Set up the mail transfer proxy
 * @param string $server The IP or domain name of the proxy server
 * @param int $port The port of the proxy server, SMTP default port 25
 * @param int $localPort The local port
 * @return boolean
*/
        public function setServer($server, $port=25) {
            if(!isset($server) || empty($server) || !is_string($server)) {
                $this->_errorMessage = "first one is an invalid parameter";
                return false;
            }
            if(!is_numeric($port)){
                $this->_errorMessage = "first two is an invalid parameter";
                return false;
            }
            $this->_sendServer = $server;
            $this->_port = $port;
            return true;
        }

        /**
 * Set up email
 * @access public
 * @param array $config Email configuration information
 * Contains email sender, recipient, subject, content, verification information of mail transfer agent
 * @return boolean
*/
        public function setMailInfo($config) {
            if(!is_array($config) || count($config) < 6){
                $this->_errorMessage = "parameters are required";
                return false;
            }

            $this->_from = $config['from'];
            $this->_to = $config['to'];
            $this->_subject = $config['subject'];
            $this->_body = $config['body'];
            $this->_userName = $config['username'];
            $this->_password = $config['password'];
            if(isset($config['isHTML'])){
                $this->_isHTML = $config['isHTML'];
            }

            return true;
        }

        /**
 * Send email
 * @access public
 * @return boolean
*/
        public function sendMail() {
            $command = $this->getCommand();
            $this->socket();

            foreach ($command as $value) {
                if($this->sendCommand($value[0], $value[1])) {
                    continue;
                }
                else{
                    return false;
                }
            }

            $this->close(); //其实这里也没必要关闭，smtp命令：QUIT发出之后，服务器就关闭了连接，本地的socket资源会自动释放
            echo 'Mail OK!';
            return true;
        }

        /**
 * Return error message
 * @return string
*/
        public function error(){
            if(!isset($this->_errorMessage)) {
                $this->_errorMessage = "";
            }
            return $this->_errorMessage;
        }

        /**
 * Return mail command
 * @access protected
 * @return array
*/
        protected function getCommand() {
            if($this->_isHTML) {
                $mail = "MIME-Version:1.0rn";
                $mail .= "Content-type:text/html;charset=utf-8rn";
                $mail .= "FROM:test<" . $this->_from . ">rn";
                $mail .= "TO:<" . $this->_to . ">rn";
                $mail .= "Subject:" . $this->_subject ."rnrn";
                $mail .= $this->_body . "rn.rn";
            }
            else{
                $mail = "FROM:test<" . $this->_from . ">rn";
                $mail .= "TO:<" . $this->_to . ">rn";
                $mail .= "Subject:" . $this->_subject ."rnrn";
                $mail .= $this->_body . "rn.rn";
            }
            $command = array(
                    array("HELO sendmailrn", 250),
                    array("AUTH LOGINrn", 334),
                    array(base64_encode($this->_userName) . "rn", 334),
                    array(base64_encode($this->_password) . "rn", 235),
                    array("MAIL FROM:<" . $this->_from . ">rn", 250),
                    array("RCPT TO:<" . $this->_to . ">rn", 250),
                    array("DATArn", 354),
                    array($mail, 250),
                    array("QUITrn", 221)
            );
            return $command;
        }

        /**
 * @access protected
 * @param string $command SMTP command sent to the server
 * @param int $code Do you expect the response returned by the server?
 * @param boolean
*/
        protected function sendCommand($command, $code) {
            echo 'Send command:' . $command . ',expected code:' . $code . '';
            //发送命令给服务器
            try{
                if(socket_write($this->_socket, $command, strlen($command))){
                    //读取服务器返回
                    $data = trim(socket_read($this->_socket, 1024));
                    echo 'response:' . $data . '';
                    if($data) {
                        $pattern = "/^".$code."/";
                        if(preg_match($pattern, $data)) {
                            return true;
                        }
                        else{
                            $this->_errorMessage = "Error:" . $data . "|**| command:";
                            return false;
                        }
                    }
                    else{
                        $this->_errorMessage = "Error:" . socket_strerror(socket_last_error());
                        return false;
                    }
                }
                else{
                    $this->_errorMessage = "Error:" . socket_strerror(socket_last_error());
                    return false;
                }
            }catch(Exception $e) {
                $this->_errorMessage = "Error:" . $e->getMessage();
            }
        }

        /**
 * Establish a network connection to the server
 * @access private
 * @return boolean
*/
        private function socket() {
            if(!function_exists("socket_create")) {
                $this->_errorMessage = "extension php-sockets must be enabled";
                return false;
            }
            //创建socket资源
            $this->_socket = socket_create(AF_INET, SOCK_STREAM, getprotobyname('tcp'));

            if(!$this->_socket) {
                $this->_errorMessage = socket_strerror(socket_last_error());
                return false;
            }

            //连接服务器
            if(!socket_connect($this->_socket, $this->_sendServer, $this->_port)) {
                $this->_errorMessage = socket_strerror(socket_last_error());
                return false;
            }
            socket_read($this->_socket, 1024);

            return true;
        }

        /**
        * 关闭socket
        * @access private
        * @return boolean
*/
        private function close() {
            if(isset($this->_socket) && is_object($this->_socket)) {
                $this->_socket->close();
                return true;
            }
            $this->_errorMessage = "no resource can to be close";
            return false;
        }
    }


    /**************************** Test ***********************************/
    $config = array(
            "from" => "********@163.com",
            "to" => "******@163.com",
            "subject" => "test",
            "body" => "test",
            "username" => "******",
            "password" => "password",
        );

    $mail = new MySendMail();

    $mail->setServer("smtp.163.com");

    $mail->setMailInfo($config);
    if(!$mail->sendMail()){
        echo $mail->error();
        return 1;
    }

PHP, HTML