send fields of form in email with php

I am trying to get all the fields of a html form and sent them by email when the submit button is pressed. But it doesn't work and I don't know why.

When I test the send button, nothing display in action.php page I don't know why. I made method="post" and action=action.php in form tag.

HTML FORM

<form action="action.php" method="POST">
   <div class="p pb-3"><strong>Feel free to contact me </strong></div>
     <div class="row mb-3">
       <div class="col">
        <div class="input-group"><span class="input-group-addon"><i class="fa fa-user-circle"></i></span>
        <input class="form-control" type="text" name="name" placeholder="Name" required="required"/>
         </div>
           </div>
            </div>
             <div class="row mb-3">
               <div class="col">
          <div class="input-group"><span class="input-group-addon"><i class="fa fa-file-text"></i></span>
     <input class="form-control" type="text" name="subject" placeholder="Subject" required="required"/>
          </div>
           </div>
            </div>
             <div class="row mb-3">
              <div class="col">
      <div class="input-group"><span class="input-group-addon"><i class="fa fa-envelope"></i></span>
      <input class="form-control" type="email" name="mail" placeholder="E-mail" required="required"/>
        </div>
         </div>
           </div>
             <div class="row mb-3">
               <div class="col">
                <div class="form-group">
 <textarea class="form-control" name="message" placeholder="Your Message" required="required"></textarea>
                 </div>
                  </div>
                    </div>
                      <div class="row">
                       <div class="col">
               <button class="btn btn-primary" type="submit" name="submit" value="Send">Send</button>
                        </div>
                      </div>
                    </form>

```.
PHP CODE
``` code
<?php
echo 'bonjour'
if(isset($_POST['submit'])){
    $name=$_POST['name'];
    $email=$_POST['email'];
    $subjectF=$_POST['subject'];
    $msg=$_POST['message'];

    $to='boussidan.raphael@gmail.com';
    $subject='Form Submission';
    $message="Name :".$name."\n"."Subject :".$subjectF."\n"."Wrote the following :"."\n\n".$msg;
    $headers="From: ".$email;

    if(mail($to, $subjectF, $message, $headers)) {
        echo "<h1>Sent Successfully! Thank you"." ".$name.", I will contact you shortly!</h1>";
        echo "Message :"." ".$message. , .$subjectF., .$email.
    }
    else{
        echo "<h1>Something went wrong!</h1>";
    }
}
?>