Allow only mails with #gmail.com ending - php

Question

This Github repository serves to add a dot (.) to a Gmail address and thus register on a site multiple times with random addresses derived from the original.
The code works fine, but it works with any domain (e.g. #house.com)
And I need to limit it to only work with #gmail.com (I tried this in my HTML) <input type="email" pattern="^[a-zA-Z0-9]+#gmail\.com$">
But I prefer it to be server side, I have no idea how to do it, I am new in PHP.
Thanks in advance.
PHP Code:
<?php
set_time_limit(0);
if(isset($_POST['email']))
{
$mail = explode('#', $_POST['email']);
$email = $mail[0];
$domain = '#'.$mail[1];
$email = ltrim($email);
$domain = ltrim($domain);
$email = rtrim($email);
$domain = rtrim($domain);
$email = stripslashes($email);
$domain = stripslashes($domain);
$email = htmlentities($email);
$domain = htmlentities($domain);
$res = addDOT($email);
echo '<div class="box"><div class="title">Total: '.sizeof($res).'</div><textarea type="text">';
foreach($res as $mcMails)
{
echo nl2br($mcMails.$domain).PHP_EOL;
}
echo '</textarea></div>';
}
function addDOT($str){
if(strlen($str) > 1)
{
$ca = preg_split("//",$str);
array_shift($ca);
array_pop($ca);
$head = array_shift($ca);
$res = addDOT(join('',$ca));
$result = array();
foreach($res as $val)
{
$result[] = $head . $val;
$result[] = $head . '.' .$val;
}
return $result;
}
return array($str);
}
?>

Answer 1

With PHP 8+ you can use str_ends_with().
function isGmail($email) {
return str_ends_with($email, '#gmail.com');
}
Or a prior PHP8+ with a classic regex
function isGmail($email) {
return preg_match("/#gmail.com\$/", $email);
}
or strpos with a negative offset
function isGmail($email) {
$pattern = '#gmail.com';
return (false !== strpos($email, $pattern, -strlen($pattern)));
}
Update
Regarding from your comment I think you want to do something like this:
$email = $_POST['email'] ?? '';
if(!isGmail($email)) {
header('Location: /');
exit();
}

Answer 2

<?php
set_time_limit(0);
if(isset($_POST['email']))
{
if(isGmail($_POST['email'])){
$mail = explode('#', $_POST['email']);
$email = $mail[0];
$domain = '#'.$mail[1];
$email = ltrim($email);
$domain = ltrim($domain);
$email = rtrim($email);
$domain = rtrim($domain);
$email = stripslashes($email);
$domain = stripslashes($domain);
$email = htmlentities($email);
$domain = htmlentities($domain);
$res = addDOT($email);
echo '<div class="box"><div class="title">Total:'.sizeof($res).'</div><textarea type="text">';
foreach($res as $mcMails)
{
echo nl2br($mcMails.$domain).PHP_EOL;
}
echo '</textarea></div>';
}
}
function addDOT($str){
if(strlen($str) > 1)
{
$ca = preg_split("//",$str);
array_shift($ca);
array_pop($ca);
$head = array_shift($ca);
$res = addDOT(join('',$ca));
$result = array();
foreach($res as $val)
{
$result[] = $head . $val;
$result[] = $head . '.' .$val;
}
return $result;
}
return array($str);
}
/**
* Check if an email is a Gmail address
* #param string $email The email address to check
* #return boolean
*/
function isGmail($email) {
$email = trim($email); // in case there's any whitespace
return mb_substr($email, -10) === '#gmail.com';
}
?>

Answer 3

Fixed. I modified the first if of the code by putting a second conditional:
if(isset($_POST['email']) and (substr($_POST['email'], -10) == '#gmail.com'))