An error occurred while sending emails via socket.

There is a problem with sending emails via socket. I think socket sending emails on the internet is basically the same as sending content to Subject & nbsp;: XXXXXXX & nbsp; that's where it is. however, after I add a tag, div & nbsp; will always be escaped, so I can put an image in the content and cannot directly receive it .... an error occurred while sending emails via socket.
I think socket-based mails are sent on the Internet.
Basically, let's
Subject:

XXXXXXX is here.
.

But after I add tags
Will always be escaped

The image in the content cannot be received directly.
What should I do ???
The code is as follows:

class aMail{
public static $smtp_prot = 25;
public static $debug = true;
public static $crlf  = "\r\n";
var $smtp_host;
var $login_name;
var $password;
var $form;
var $to;
var $err;
var $message;
var $socket;
function __construct($options=""){
if($options == "" || !is_array($options)){
return false;
}
foreach($options as $key=>$val){
$this->$key = $val;
}
}

function sendMail(){ 
$this->socket = fsockopen($this->smtp_host,self::$smtp_prot);
$socket = $this->socket;
$crlf   = self::$crlf;
stream_set_blocking($socket,true);
$this->message = fgets($socket,512);
echo $this->message;
if(!$this->print_messsage("/^220/","connect fail")){
return false;
}

fputs($socket,"EHLO 127.0.0.1 ".$crlf);
$this->message = fgets($socket, 512);
if(!$this->print_messsage("/^2/","EHLO fail")){
return false;
}

fputs($socket,"AUTH LOGIN".$crlf);
$this->message = fgets($socket, 512);
$this->print_messsage("/^2/","AUTH LOGIN fail");

fputs($socket,base64_encode($this->login_name).$crlf);
$this->message = fgets($socket, 512);
$this->print_messsage("/^2/","login_name fail");

fputs($socket,base64_encode($this->password).$crlf);
$this->message = fgets($socket, 512);
$this->print_messsage("/^2/","password fail");

fputs($socket,"MAIL FROM: <".$this->from.">".$crlf);
$this->message = fgets($socket, 512);
$this->print_messsage("/^2/","from fail");

fputs($socket,"RCPT TO: <".$this->to.">".$crlf);
$this->message = fgets($socket, 512);
$this->print_messsage("/^334|^2/","to fail");

fputs($socket,"DATA".$crlf);
$this->message = fgets($socket, 512);
$this->print_messsage("/^334|^2/","DATA fail");

$html = implode("",array(
"To: ".$this->to.$crlf,
"From: ".$this->from.$crlf,
"Subject: ".$this->subject.$crlf.$crlf,
$this->content.$crlf.".".$crlf,
));

fputs($socket,$html);
$this->message = fgets($socket, 512);
$this->print_messsage("/^2/","html fail");

fputs($socket, "QUIT".$crlf);
$this->message=fgets($socket,512);
$this->print_messsage("/^2/","QUIT fail");
}
function print_messsage($reg="",$err=""){
$message = $this->message;
if(preg_match($reg,$message)<=0){
$this->err = $err."___".$message."--------------";
echo $err."___".$message."--------------
";
return false;
}
if(self::$debug){
echo $this->message."
";
}
return true;
}
}
$mail_options = array(
"smtp_host"=>"smtp.sina.com.cn",
"login_name"=>"ycwtt0527",