Ayuda en formulario de contacto

Hola buenas.

Acabo de crear un formulario de contacto php html y detecto como pruebas que estoy haciendo que cuando en el campo de email se escribe algún correo que no sea Gmail no recibo la solicitud, he cambiado en el archivo send_from_email.php la recepción de correo de yahoo a Gmail y este no es el problema.

emeail.html

configuracion email.html

Código

<!doctype htlm>
<html lang="es">
    <head>  
        <title>email</title>                   
        <link rel="stylesheet" type="text/css" href="email_general.css">                             
        <meta name="viewport" content="width=device-width; user-scalable=no; initial-scale=1; maximun-scale=1"> 
	</head>
 
    <body> 
<br>
<br>
<ul class="flex-container1">
 <li class="item1" id="item">
   <form><b>Rellenar todos los campos obligatorios *</b></form>
   <form><b>antes de mandar el email.</b></form>
<br>   
     <form name="contactform" method="post" action="send_form_email.php">
<table width="70%"> <!-- 330 PX; -->
<tr>
 <td valign="top">
  <label for="first_name">Nombre*</label>
 </td>
 <td valign="top">
  <input  type="text" name="first_name" maxlength="50" size="24">
 </td>
</tr>
<tr>
 <td valign="top"">
  <label for="last_name">Apellidos*</label>
 </td>
 <td valign="top">
  <input  type="text" name="last_name" maxlength="50" size="24">
 </td>
</tr>
<tr>
 <td valign="top">
  <label for="email">Email*</label>
 </td>
 <td valign="top">
  <input  type="text" name="email" maxlength="80" size="24">
 </td>
</tr>
<tr>
 <td valign="top">
  <label for="telephone">Telefono*</label>
 </td>
 <td valign="top">
  <input  type="text" name="telephone" maxlength="30" size="24">
 </td>
</tr>
<tr>
 <td valign="top">
  <label for="comments">Commentario*</label>
 </td>
 <td valign="top">
  <textarea  name="comments" maxlength="1000" cols="25" rows="10"></textarea>
 </td>
</tr>
<tr>
 <td colspan="2" style="text-align:center">
  <input type="submit" value="Enviar">   <a href="https://xxxxxxxxxxxxxxx.es"><b>Web Inicio</b></a>
 </td>
</tr>
</table>
</form>
    </li>
 
	</body>	
</htlm>

codigo php

Código

<?php
if(isset($_POST['email'])) {
 
    // EDIT THE 2 LINES BELOW AS REQUIRED
    $email_to = "xxxxxxxxxxxx@yahoo.es"; /*you@yourdomain.com */
    $email_subject = "xxxxxxxxxxxxxx"; /*Your email subject line */
 
    function died($error) {
        // your error code can go here
        echo "We are very sorry, but there were error(s) found with the form you submitted. ";
        echo "These errors appear below.<br /><br />";
        echo $error."<br /><br />";
        echo "Please go back and fix these errors.<br /><br />";
        die();
    }
 
 
    // validation expected data exists
    if(!isset($_POST['first_name']) ||
        !isset($_POST['last_name']) ||
        !isset($_POST['email']) ||
        !isset($_POST['telephone']) ||
        !isset($_POST['comments'])) {
        died('We are sorry, but there appears to be a problem with the form you submitted.');       
    }
 
 
 
    $first_name = $_POST['first_name']; // required
    $last_name = $_POST['last_name']; // required
    $email_from = $_POST['email']; // required
    $telephone = $_POST['telephone']; // not required
    $comments = $_POST['comments']; // required
 
    $error_message = "";
    $email_exp = '/^[A-Za-z0-9._%-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,4}$/';
 
  if(!preg_match($email_exp,$email_from)) {
    $error_message .= 'The Email Address you entered does not appear to be valid.<br />';
  }
 
    $string_exp = "/^[A-Za-z .'-]+$/";
 
  if(!preg_match($string_exp,$first_name)) {
    $error_message .= 'The First Name you entered does not appear to be valid.<br />';
  }
 
  if(!preg_match($string_exp,$last_name)) {
    $error_message .= 'The Last Name you entered does not appear to be valid.<br />';
  }
 
  if(strlen($comments) < 2) {
    $error_message .= 'The Comments you entered do not appear to be valid.<br />';
  }
 
  if(strlen($error_message) > 0) {
    died($error_message);
  }
 
    $email_message = "Form details below.\n\n";
 
 
    function clean_string($string) {
      $bad = array("content-type","bcc:","to:","cc:","href");
      return str_replace($bad,"",$string);
    }
 
 
 
    $email_message .= "First Name: ".clean_string($first_name)."\n";
    $email_message .= "Last Name: ".clean_string($last_name)."\n";
    $email_message .= "Email: ".clean_string($email_from)."\n";
    $email_message .= "Telephone: ".clean_string($telephone)."\n";
    $email_message .= "Comments: ".clean_string($comments)."\n";
 
// create email headers
$headers = 'From: '.$email_from."\r\n".
'Reply-To: '.$email_from."\r\n" .
'X-Mailer: PHP/' . phpversion();
@mail($email_to, $email_subject, $email_message, $headers);  
?>
 
<!-- include your own success html here -->
 
Gracias por contactarnos. Estaremos en contacto con usted muy pronto.
 
<?php
 
}
?>

Salud2.