How to make an application come to telegrams and mail?

Question

AJAX

I tried to make the letters come to the mail and telegrams, but nothing happened. Erase code. Here is the code that sends the email.

<?php 
if (!empty($_POST['name']) AND !empty($_POST['email']) AND !empty($_POST['message'])) 
{
    
         
    $theme = "Новое сообщение с сайта";             
             
    $letter = "Данные сообщения:";
    $letter .="\n\n";
    $letter .="Имя: ".$_POST['name'];
    $letter .="\nEmail: ".$_POST['email'];
    $letter .="\nТелефон: ".$_POST['phone'];
    $letter .="\nСообщение: ".$_POST['message'];
    
    if (mail("[email protected]", $theme, $letter, $headers)){
      header("Location: /testform/thankyou.php");
    } else {
      header("Location: /testform");
    }  
              
} else {
  header("Location: /testform");
}

Guys please help!!