telnet smtp.163.com 25 

Trying 220.181.12.16...
Connected to smtp.163.com.
Escape character is '^]'.
220 163.com Anti-spam GT for Coremail System (163com[20141201])

HELO smtp.163.com

class Mailer
{
  private $host;
  private $port = 25;
  private $user;
  private $pass;
  private $debug = false;
  private $sock;

  public function __construct($host,$port,$user,$pass,$debug = false)
  {
    $this->host = $host;
    $this->port = $port;
    $this->user = base64_encode($user); //用户名密码一定要使用base64编码才行
    $this->pass = base64_encode($pass);
    $this->debug = $debug;
  //socket连接
    $this->sock = fsockopen($this->host,$this->port);
    if(!$this->sock){
      exit('出错啦');
    }
  //读取smtp服务返回给我们的数据
    $response = fgets($this->sock);
    $this->debug($response);
        //如果响应中有220返回码，说明我们连接成功了
    if(strstr($response,'220') === false){
      exit('出错啦');
    }
  }
//发送SMTP指令，不同指令的返回码可能不同
  public function execCommand($cmd,$return_code){
    fwrite($this->sock,$cmd);

    $response = fgets($this->sock);
//输出调试信息
    $this->debug('cmd:'.$cmd .';response:'.$response);
    if(strstr($response,$return_code) === false){
      return false;
    }
    return true;
  }

  public function sendMail($from,$to,$subject,$body){
//detail是邮件的内容，一定要严格按照下面的格式，这是协议规定的
    $detail = 'From:'.$from."\r\n";
    $detail .= 'To:'.$to."\r\n";
    $detail .= 'Subject:'.$subject."\r\n";
    $detail .= 'Content-Type: Text/html;'."\r\n";
    $detail .= 'charset=gb2312'."\r\n\r\n";
    $detail .= $body;
    $this->execCommand("HELO ".$this->host."\r\n",250);
    $this->execCommand("AUTH LOGIN\r\n",334);
    $this->execCommand($this->user."\r\n",334);
    $this->execCommand($this->pass."\r\n",235);
    $this->execCommand("MAIL FROM:<".$from.">\r\n",250);
    $this->execCommand("RCPT TO:<".$to.">\r\n",250);
    $this->execCommand("DATA\r\n",354);
    $this->execCommand($detail."\r\n.\r\n",250);
    $this->execCommand("QUIT\r\n",221);
  }

  public function debug($message){
    if($this->debug){
      echo '<p>Debug:'.$message . PHP_EOL .'</p>';
    }
  }

  public function __destruct()
  {
    fclose($this->sock);
  }

}

$port = 25;
$user = 'username'; //请替换成你自己的smtp用户名
$pass = 'pass'; //请替换成你自己的smtp密码
$host = 'smtp.163.com';
$from = 'xxxxx@163.com'; 
$to = 'xxxx@qq.com';
$body = 'hello world';
$subjet = '我是标题';
$mailer = new Mailer($host,$port,$user,$pass,true);
$mailer->sendMail($from,$to,$subjet,$body);

Debug:220 163.com Anti-spam GT for Coremail System (163com[20141201])

Debug:cmd:HELO smtp.163.com ;response:250 OK

Debug:cmd:AUTH LOGIN ;response:334 dXNlcm5hbWU6

Debug:cmd:aXR6aG91anVuYmxvZ0AxNjMuY29t ;response:334 UGFzc3dvcmQ6

Debug:cmd:QzBjSGRRNe32xiNGFYUE5oag== ;response:235 Authentication successful

Debug:cmd:MAIL FROM: ;response:250 Mail OK

Debug:cmd:RCPT TO:<380472723@qq.com> ;response:250 Mail OK

Debug:cmd:DATA ;response:354 End data with .

Debug:cmd:From:itzhoujunblog@163.com To:380472723@qq.com Subject:我是标题 Content-Type: Text/html; charset=gb2312 hello world . ;response:250 Mail OK queued as smtp11,D8CowACXHE5APdNYCo0hAQ--.19144S2 1490238785

Debug:cmd:QUIT ;response:221 Bye