How to implement the function of sending emails in php smtp

<?php
header("Content-Type: text/html; charset=utf-8");
 
class smtp
{
 /* Public Variables */
 var $smtp_port;
 var $time_out;
 var $host_name;
 var $log_file;
 var $relay_host;
 var $debug;
 var $auth;
 var $user;
 var $pass;
 
 /* Private Variables */ 
 var $sock;
 
 /* Constractor */
 function smtp($relay_host = "", $smtp_port = 25,$auth = false,$user,$pass)
 {
  $this->debug = FALSE;
  $this->smtp_port = $smtp_port;
  $this->relay_host = $relay_host;
  $this->time_out = 30; //is used in fsockopen() 
  $this->auth = $auth;//auth
  $this->user = $user;
  $this->pass = $pass;
  $this->host_name = "localhost"; //is used in HELO command 
  $this->log_file = "";
  $this->sock = FALSE;
}
 
 /* Main Function */
 function sendmail($to, $from, $subject = "", $body = "", $mailtype, $cc = "", $bcc = "", $additional_headers = "")
 {
  $mail_from = $this->get_address($this->strip_comment($from));
  $body = preg_replace("/(^|(\r\n))(\.)/", "\1.\3", $body);
  $header = "MIME-Version:1.0\r\n";
  if($mailtype=="HTML")
  {
   $header .= "Content-Type:text/html\r\n";
  }
  $header .= "To: ".$to."\r\n";
  if ($cc != "") 
  {
   $header .= "Cc: ".$cc."\r\n";
  }
  $header .= "From: $from<".$from.">\r\n";
  $header .= "Subject: ".$subject."\r\n";
  $header .= $additional_headers;
  $header .= "Date: ".date("r")."\r\n";
  $header .= "X-Mailer:By Redhat (PHP/".phpversion().")\r\n";
  list($msec, $sec) = explode(" ", microtime());
  $header .= "Message-ID: <".date("YmdHis", $sec).".".($msec*1000000).".".$mail_from.">\r\n";
  $TO = explode(",", $this->strip_comment($to));
 
  if ($cc != "") 
  {
   $TO = array_merge($TO, explode(",", $this->strip_comment($cc)));
   }
  if ($bcc != "") 
  {
   $TO = array_merge($TO, explode(",", $this->strip_comment($bcc)));
  }
  $sent = TRUE;
  foreach ($TO as $rcpt_to) 
  {
   $rcpt_to = $this->get_address($rcpt_to);
   if (!$this->smtp_sockopen($rcpt_to)) 
   {
    $this->log_write("Error: Cannot send email to ".$rcpt_to."\n");
    $sent = FALSE;
    continue;
   }
   if ($this->smtp_send($this->host_name, $mail_from, $rcpt_to, $header, $body)) 
   {
    $this->log_write("E-mail has been sent to <".$rcpt_to.">\n");
   } 
   else 
   {
    $this->log_write("Error: Cannot send email to <".$rcpt_to.">\n");
    $sent = FALSE;
   }
   fclose($this->sock);
   $this->log_write("Disconnected from remote host\n");
  }
  return $sent;
 }
 
 /* Private Functions */
 function smtp_send($helo, $from, $to, $header, $body = "")
 {
  if (!$this->smtp_putcmd("HELO", $helo)) 
  {
   return $this->smtp_error("sending HELO command");
  }
 
  #auth
  if($this->auth)
  {
   if (!$this->smtp_putcmd("AUTH LOGIN", base64_encode($this->user))) 
   {
    return $this->smtp_error("sending HELO command");
   }
   if (!$this->smtp_putcmd("", base64_encode($this->pass))) 
   {
    return $this->smtp_error("sending HELO command");
   }
  }
  if (!$this->smtp_putcmd("MAIL", "FROM:<".$from.">")) 
  {
   return $this->smtp_error("sending MAIL FROM command");
  }
  if (!$this->smtp_putcmd("RCPT", "TO:<".$to.">")) 
  {
   return $this->smtp_error("sending RCPT TO command");
  }
  if (!$this->smtp_putcmd("DATA"))
  {
   return $this->smtp_error("sending DATA command");
  }
  if (!$this->smtp_message($header, $body)) 
  {
   return $this->smtp_error("sending message");
  }
  if (!$this->smtp_eom())
  {
   return $this->smtp_error("sending <CR><LF>.<CR><LF> [EOM]");
  }
  if (!$this->smtp_putcmd("QUIT")) 
  {
   return $this->smtp_error("sending QUIT command");
  }
  return TRUE;
 }
 
 function smtp_sockopen($address)
 {
  if ($this->relay_host == "") 
  {
   return $this->smtp_sockopen_mx($address);
  } 
  else
  {
   return $this->smtp_sockopen_relay();
  }
 }
 
 function smtp_sockopen_relay()
 {
  $this->log_write("Trying to ".$this->relay_host.":".$this->smtp_port."\n");
  $this->sock = @fsockopen($this->relay_host, $this->smtp_port, $errno, $errstr, $this->time_out);
  if (!($this->sock && $this->smtp_ok())) 
  {
   $this->log_write("Error: Cannot connenct to relay host ".$this->relay_host."\n");
   $this->log_write("Error: ".$errstr." (".$errno.")\n");
   return FALSE;
  }
  $this->log_write("Connected to relay host ".$this->relay_host."\n");
  return TRUE;;
 }
 
 function smtp_sockopen_mx($address)
 {
  $domain = preg_replace("^.+@([^@]+)$", "\1", $address);
  if (!@getmxrr($domain, $MXHOSTS)) 
  {
   $this->log_write("Error: Cannot resolve MX \"".$domain."\"\n");
   return FALSE;
  }
  foreach ($MXHOSTS as $host) 
  {
   $this->log_write("Trying to ".$host.":".$this->smtp_port."\n");
   $this->sock = @fsockopen($host, $this->smtp_port, $errno, $errstr, $this->time_out);
   if (!($this->sock && $this->smtp_ok())) 
   {
    $this->log_write("Warning: Cannot connect to mx host ".$host."\n");
    $this->log_write("Error: ".$errstr." (".$errno.")\n");
    continue;
   }
   $this->log_write("Connected to mx host ".$host."\n");
   return TRUE;
  }
  $this->log_write("Error: Cannot connect to any mx hosts (".implode(", ", $MXHOSTS).")\n");
  return FALSE;
 }
 
 function smtp_message($header, $body)
 {
  fputs($this->sock, $header."\r\n".$body);
  $this->smtp_debug("> ".str_replace("\r\n", "\n"."> ", $header."\n> ".$body."\n> "));
  return TRUE;
 }
 
 function smtp_eom()
 {
  fputs($this->sock, "\r\n.\r\n");
  $this->smtp_debug(". [EOM]\n");
  return $this->smtp_ok();
 }
 
 function smtp_ok()
 {
  $response = str_replace("\r\n", "", fgets($this->sock, 512));
  $this->smtp_debug($response."\n");
  if (!preg_match("/^[23]/", $response)) 
  {
   fputs($this->sock, "QUIT\r\n");
   fgets($this->sock, 512);
   $this->log_write("Error: Remote host returned \"".$response."\"\n");
   return FALSE;
  }
  return TRUE;
 }
 
 function smtp_putcmd($cmd, $arg = "")
 {
  if ($arg != "") 
  {
   if($cmd=="") 
   {
    $cmd = $arg;
   }
   else
   {
    $cmd = $cmd." ".$arg;
   }
  }
  fputs($this->sock, $cmd."\r\n");
  $this->smtp_debug("> ".$cmd."\n");
  return $this->smtp_ok();
 }
 
 function smtp_error($string)
 {
  $this->log_write("Error: Error occurred while ".$string.".\n");
  return FALSE;
 }
 
 function log_write($message)
 {
  $this->smtp_debug($message);
  if ($this->log_file == "")
  {
   return TRUE;
  }
  $message = date("M d H:i:s ").get_current_user()."[".getmypid()."]: ".$message;
  if (!@file_exists($this->log_file) || !($fp = @fopen($this->log_file, "a"))) 
  {
   $this->smtp_debug("Warning: Cannot open log file \"".$this->log_file."\"\n");
   return FALSE;;
  }
  flock($fp, LOCK_EX);
  fputs($fp, $message);
  fclose($fp);
  return TRUE;
 }
 
 function strip_comment($address)
 {
  $comment = "/\([^()]*\)/";
  while (preg_match($comment, $address)) 
  {
   $address = preg_replace($comment, "", $address);
  }
  return $address;
 }
 
 function get_address($address)
 {
  $address = preg_replace("/([ \t\r\n])+/", "", $address);
  $address = preg_replace("/^.*<(.+)>.*$/", "\1", $address);
  return $address;
 }
 
 function smtp_debug($message)
 {
  if ($this->debug) 
  {
   echo $message;
  }
 }
 
}
?>

<?php
header("Content-Type: text/html; charset=utf-8");
 
//引入发送邮件类
require("smtp.php");
//使用163邮箱服务器
$smtpserver = "smtp.163.com";
//163邮箱服务器端口
$smtpserverport = 25;
//你的163服务器邮箱账号
$smtpusermail = "xxx@163.com";
//收件人邮箱
$smtpemailto = "xxx@qq.com";
 
//你的邮箱账号(去掉@163.com)
$smtpuser = "xxx";//你的163邮箱去掉后面的163.com
//你的邮箱密码
$smtppass = "xxx"; //你的163邮箱SMTP的授权码，千万不要填密码！！！
 
//邮件主题
$mailsubject = "测试邮件发送";
//邮件内容
$mailbody = "PHP+MySQL";
//邮件格式（HTML/TXT）,TXT为文本邮件
$mailtype = "TXT";
//这里面的一个true是表示使用身份验证,否则不使用身份验证.
$smtp = new smtp($smtpserver,$smtpserverport,true,$smtpuser,$smtppass);
//是否显示发送的调试信息
$smtp->debug = TRUE;
//发送邮件
$smtp->sendmail($smtpemailto, $smtpusermail, $mailsubject, $mailbody, $mailtype);
 
?>