Exclude a specific email address from form submission - php

Question

I have seen this question asked elsewhere but am unsure of how to put some validation into my particular form which will exclude a particular email address. I would like the form to be rejected if an email address is entered, lets say anything#anything.com. Please see code below. There is more but i believe this is the relevant part...
$errors = array();
// Remove $_COOKIE elements from $_REQUEST.
if(count($_COOKIE)){
foreach(array_keys($_COOKIE) as $value){
unset($_REQUEST[$value]);
}
}
// Validate email field.
if(isset($_REQUEST['email']) && !empty($_REQUEST['email']))
{
$_REQUEST['email'] = trim($_REQUEST['email']);
if(substr_count($_REQUEST['email'],"#") != 1 ||
stristr($_REQUEST['email']," ") ||
stristr($_REQUEST['email'],"\\") ||
stristr($_REQUEST['email'],":") ){
$errors[] = "Email address is invalid";
}
else{
$exploded_email = explode("#",$_REQUEST['email']);
if (empty($exploded_email[0]) ||
strlen($exploded_email[0]) > 64 ||
empty($exploded_email[1])){
$errors[] = "Email address is invalid";
}
else{
if(substr_count($exploded_email[1],".") == 0){
$errors[] = "Email address is invalid";
}
else{
$exploded_domain = explode(".",$exploded_email[1]);
if(in_array("",$exploded_domain)){
$errors[] = "Email address is invalid";
}
else{
foreach($exploded_domain as $value){
if(strlen($value) > 63 ||
!preg_match('/^[a-z0-9-]+$/i',$value)){
$errors[] = "Email address is invalid";
break;
}
}
}
}
}
}
}

Answer 1

If I understand your code, the goal of the main part is to validate the format of the email given by the user.
First of all, there is a built-in php function for this ( PHP >= 5.2 ) : filter_var(). You can replace all this block of code with :
$email = trim($_REQUEST['email']);
if (!filter_var($email_a, FILTER_VALIDATE_EMAIL)) {
$errors[] = "Email address is invalid";
}
Then, if you want to check the email is not in a blacklist, just do something like this :
// Fill this array the way you want : hard-write it, fetch from database...
$blacklist = array("email1#gmail.com", "email2#gmail.com");
// Put in lower case for easiest comparison
$email = strtolower($email);
if (in_array($email, $blacklist)) {
$errors[] = "Email address is blacklisted";
}