在PHP联系表单中配置SMTP

I'm using a bootstrap theme which came with a PHP contact form for my portfolio. When I used it on my old web hosting, it worked no problem. However, now that I'm using siteground, the messages arrive in my inbox with a delay, and sometimes not at all.

According to Siteground, I have to use SMTP in my contact form, but I have no idea how to do so. Would you be able to help me out?

  //Removed empty($_POST['phone']) ||

  $name = strip_tags(htmlspecialchars($_POST['name']));
  $email = strip_tags(htmlspecialchars($_POST['email']));
  //$phone = strip_tags(htmlspecialchars($_POST['phone']));
  $message = strip_tags(htmlspecialchars($_POST['message']));

  // Create the email and send the message
  $to = "benibargera@gmail.com"; // Add your email address inbetween the "" replacing yourname@yourdomain.com - This is where the form will send a message to.
  $subject = "Website Contact Form:  $name";
  $body = "You have received a new message from your website contact form.

"."Here are the details:

Name: $name

Email: $email

Phone: $phone

Message:
$message";
  $header = "From: my@email.com
"; // This is the email address the generated message will be from. We recommend using something like noreply@yourdomain.com.
  $header .= "Reply-To: $email";

  if(!mail($to, $subject, $body, $header))
    http_response_code(500);
  ?>