My PHP form submits but does not validate the email address - php

Question

I am an eager novice with PHP so please forgive my errors as I am learning as I go. Basically, I am building a simple contact form for my website and have successfully been able to have the form send the user's first and last name, subject, email address and message. I am using a second file, "form_process.php" to process the form data from "index.php".
The problem is that the email address does not seem to be validating and will send any words typed. I would greatly appreciate it if some more seasoned eyes could take a look and help me sort this out. Thank you in advance.
Michael.
HTML:
<div id="form">
<form action="form_process.php" method="post" enctype="multipart/form-data">
<p>
<input type="text" maxlength="100" size="50" name="fName" value="<?php echo $stored_fName;?>" placeholder="First Name" />
</p>
<p>
<input type="text" maxlength="100" size="50" name="lName" value="<?php echo $stored_lName;?>" placeholder="Last Name" />
</p>
<p>
<input type="text" maxlength="80" size="50" name="email" value="<?php echo $stored_email;?>" placeholder="Email Address" />
</p>
<p>
<input type="text" maxlength="100" size="50" name="subject" value="<?php echo $stored_subject;?>" placeholder="Subject" />
</p>
<p>
<textarea name="message" rows="6" cols="38" placeholder="Message"></textarea>
</p>
<br />
<input type="submit" value="Submit" name="submit" />
<input type="reset" value="Clear" name="clear">
</form>
</div>
<!-- form ends -->
PHP: "form_process.php"
<?php
session_start();
// Report all PHP errors
error_reporting(E_ALL);
//use $_POST to to store data from submitted form into these variables
$fName = check_input($_POST['fName']);
$lName = check_input($_POST['lName']);
$sender = check_input($_POST['email']);
$subject = check_input($_POST['subject']);
$message = check_input($_POST['message']);
//check_input function to strip unnessessary characters and sanitize user data
function check_input($data)
{
$data = trim($data);
$data = stripslashes($data);
$data = htmlspecialchars($data);
return $data;
}
$name = $fName ." ". $lName;//concatenating first and last names to new name variable
$sanitizedEmail = filter_var($sender, FILTER_SANITIZE_EMAIL);
//generates error messages on index.php if form fields left blank
if ($fName == ''){
header("Location:index.php?message=1");
exit();
}
if ($lName == ''){
header("Location:index.php?message=2");
exit();
}
if ($sender == ''){
header("Location:index.php?message=3");
exit();
}
if ($subject == ''){
header("Location:index.php?message=4");
exit();
}
if ($message == ''){
header("Location:index.php?message=5");
exit();
}
//headers
$headers = "MIME-Version: 1.0" . "\r\n";
$headers .= "Content-type:text/html;charset=iso-8859-1" . "\r\n";
$headers .= $name . "\r\n";
$headers .= "From:" . " " . $sanitizedEmail . "\r\n";
//mail function
$to = "me#myemail.com";
$subject = $subject;
$message = $message;
//send message
$send_message = mail($to,$subject,$message,$headers);
if($send_message){
header("Location:index.php?message=6");
}else {
header("Location:index.php?message=9");
exit();
}
?>
"index.php" error messages:
<?php
//all fields empty until user inputs data for session to store
$stored_fName = '';//init as NULL
$stored_lName = '';//init as NULL
$stored_email = '';//init as NULL
$stored_subject = '';//init as NULL
$stored_message = '';//init as NULL
//session data used to repopulate form fields if any info is missing or incorrect
if (isset($_SESSION['fName'])){
$stored_fName = $_SESSION['fName'];
}
if (isset($_SESSION['lName'])){
$stored_lName = $_SESSION['lName'];
}
if (isset($_SESSION['email'])){
$stored_email = $_SESSION['email'];
}
if (isset($_SESSION['subject'])){
$stored_subject = $_SESSION['subject'];
}
if (isset($_SESSION['message'])){
$stored_message = $_SESSION['message'];
}
//error messages displayed to user if text fields have been left blank
$_GET['message'];
if ($_GET['message'] == 1) {//first name
echo "<strong>Please type your first name.</strong>";
}
if ($_GET['message'] == 2) {//last name
echo "<strong>Please type your last name.</strong>";
}
if ($_GET['message'] == 3){//email address
echo "<strong>Please type an email address.</strong>";
}
if ($_GET['message'] == 4){//subject
echo "<strong>Please type a subject.</strong>";
}
if ($_GET['message'] == 5){//message text
echo "<strong>Please type your message.</strong>";
}
if ($_GET['message'] == 6){//message success from form_process.php
echo "<strong>Your message was sent successfully. Thank you.</strong>";
}
if ($_GET['message'] == 9){
echo "<strong>I'm sorry but your message was not sent. Please try again, thank you.</strong>";
}
?>

Answer 1

You should be using it like this:
if(filter_var($email, FILTER_VALIDATE_EMAIL)){
// is email
$sender = $email;
}else{
// isn't email
$sender = '';
}
Read more about PHP Validate Filters