php Socket sends an email to verify the actual validity of the email address rather than the format

/*Please respect the success of other people’s work and keep this copyright information, thank you!
Author: Xiaoluzhu 3.3
Yangfan corrected something: It has been noted in the code with comments. This code now has no problem sending letters to qq~
*/
set_time_limit(120);

class smtp_mail
{
 var $host ; //Host
 var $port; //The port is generally 25
 var $user; //SMTP authentication account
 var $pass; //Authentication password
 var $debug = false; //Whether to display session information with the server ?
 var $conn;
 var $result_str; //Result
 var $in; //Command sent by the client
 var $from; //Source mailbox
 var $to; //Destination mailbox
 var $subject; // Topic
 var $body; //Content
 function smtp_mail($host,$port,$user,$pass,$debug=false)
 {
 $this->host = $host;
 $this->port = $port;
 $this->user = base64_encode($user);
 $this->pass = base64_encode($pass);
 $this->debug = $debug;
 $this->socket = socket_create (AF_INET, SOCK_STREAM, SOL_TCP); //Please refer to the manual for specific usage
 if($this->socket)
 {
 $this->result_str = "Create SOCKET:".socket_strerror(socket_last_error());
 $this->debug_show($this->result_str);
 }
 else
 {
 exit("Initialization failed, please check your network connection and parameters");
 }
 $this->conn = socket_connect($this->socket,$this->host,$this->port);
 if($this->conn)
 {
 $this->result_str = "Create SOCKET connection:" .socket_strerror(socket_last_error());
 $this->debug_show($this->result_str);
 }
 else
 {
 exit("Initialization failed, please check your network connection and parameters");
 }
 $this->result_str = "Server response: ".socket_read ($this->socket, 1024)."";
 $this->debug_show( $this->result_str);

 }
 function debug_show($str)
 {
 if($this->debug)
 {
 echo $str."rn";
 }
 }
 function send($from,$to,$subject,$body)
 {
 if($from == "" || $to == "")
 {
 exit("Please enter your email address");
 }
 if($subject == "") $sebject = "No title";
 if($body == "") $body = "No content";
 $this->from = $from;
 $this ->to = $to;
 $this->subject = $subject;
 $this->body = $body;

 //Yangfan modified part of the code
 $All = "From:<".$ this->from.">rn";
 $All .= "To:<".$this->to.">rn";
 $All .= "Subject:".$this- >subject."rnrn";
 $All .= $this->body;
 /*
 If you process the content of $All, you can send MIME emails
 But you still need to add a lot of programs
 */

 //The following is a session with the server
 $this->in = "EHLO HELOrn";
 $this->docommand();

 $this->in = "AUTH LOGINrn";
 $ this->docommand();

 $this->in = $this->user."rn";
 $this->docommand();

 $this->in = $this- >pass."rn";
 $this->docommand();

 // $this->in = "MAIL FROM:".$this->from."rn";
 $this- >in = "MAIL FROM:<".$this->from.">rn"; // Yangfan modified
 $this->docommand();

 // $this->in = "RCPT TO:".$this->to."rn";
 $this->in = "RCPT TO:<".$this->to.">rn"; //Sail modification
 $this->docommand();

 $this->in = "DATArn";
 $this->docommand();

 $this->in = $All."rn.rn" ;
 $this->docommand();

 $this->in = "QUITrn";
 $this->docommand();

 //End, close the connection

 }
 function docommand()
 {
 socket_write ($this->socket, $this->in, strlen ($this->in));
 $this->debug_show("Client command: ".$this-> in);
 $this->result_str = "Server response: ".socket_read ($this->socket, 1024)."";
 $this-> ;debug_show($this->result_str);
 }
}
?>

php code

//Test page
include "smtp_mail.php";

//When you use this class, just modify it to your own mailbox
$smtp =new smtp_mail("smtp.qq.com","25","yourmail@qq.com","Your password",true);
//If you need to display session information, please change the above to
/ /$smtp = new smtp_mail("smtp.qq.com","25","your qq.com account","your password",true);
$smtp->send("yourmail@qq .com","yourmail@qq.com","Hello","Test Email");
?>

Instead of sending email, php