For starters, your code needs tidying up, so I have done this for you. Also, what do you mean it's not working? You won't know if it is working because you haven't told it to tell you. You have just set the variable $su and not done anything with it. Here is what your code should look like:
<?php
$su="";
if(isset($_POST['submit']))
{
$name = $_POST['name'];
$email = $_POST['email'];
$subject = $_POST['subject'];
$message = $_POST['message'];
$to = 'jikkas@gmail.com';
$subject = 'the subject';
$message = 'Subject: '.$subject.'</br></br></br>'.$message;
$headers = 'Name: '.$name.'</br>'.'Email: '.$email;
$send = mail($to, $subject, $message, $headers);
if($send)
{
$su = "Thanks for being with us...";
echo $su;
}
else
{
$su = "Error: unable to send";
echo $su;
//See note below
}
}
?>
I have included an else statement in there just as an example if you want to use your own error handling function. However, error_reporting should ideally be set to E_ALL to ensure you are capturing any errors that may be occurring. Also, ensure you have the correct mail settings in your php.ini. Look here for more details on mail settings in php.ini.
I would recommend running the following script:
<?php
// Set error reporting level to all errors
error_reporting(E_ALL);
// View php.ini and look for the mail settings
phpinfo();
?>
Hope this helps!