Prevent Specific Email Registration Wordpress.org - wordpress

Question

So I'm looking for a way to prevent a specific email from registering an account on my website. It's a wordpress.org site.
I tried the Ban Hammer plugin, but it won't work.
I'm not looking for Comments, but for the site proper. Like a code I can put in functions.php or someplace and when this specific email is used to try and register an account on my site, to get an error.
Not an entire email domain, for example, #gmail.com. But a specific email, for example, stack#gmail.com.
Anyone knows how to do that?
EDIT: I found this tutorial here: http://www.davidtiong.com/block-spam-registrations-on-wordpress/
I tried adding this in Functions.php file right above the last ?> at the very bottom of the file:
function dtwd_blocked_emails($user_email) {
$dtwd_blocked_list = array("slojehupri#thrma.com", );
$user_email_split = explode('#', $user_email); $user_email_domain = $user_email_split[1];
if (in_array($user_email_domain, $dtwd_blocked_list)) {
//Return 1, for detection
return 1;
} else {
//Return 0 for no detection
return 0;
}
}
And I also added this in register.php of my theme:
elseif ( dtwd_blocked_emails( $user_email ) == 1) {
$errors->add( 'blocked_email', __( '<strong>ERROR</strong>: This email is not allowed.' ) );
}
And I added the same code in login.php of my theme.
And then I tried registering an account with this email (which should be blocked now): slojehupri#thrma.com
The site allowed me to register, and it allowed me to login. The email should've been blocked now and return an error when I try to register and/or login with it.

Answer 1

I'm not really sure how that function is supposed to work (it's not even hooked into anything...). I haven't tested this, but it sounds as simple as validating the email when the registration_errors filter hook is run. From the Codex:
The registration_errors filter hook filters the errors encountered when a new user is being registered. If any errors are present in $errors, this will abort the user's registration.
This sounds exactly like what you want to do (abort registration if the user email is in your blacklist). Again, this hasn't been tested, but I'd try something like the following in functions.php:
function so_32767928_blacklisted_user( $errors, $sanitized_user_login, $user_email ) {
// One or more blacklisted emails to validate against
$blacklist = array( 'slojehupri#thrma.com', );
// If the user trying to register is in the blacklist, add an error message
if ( in_array( $user_email, $blacklist ) ) {
$errors->add( 'blacklist_error', '<strong>ERROR</strong>: This email is not allowed to register on this site.' );
}
// Always return $errors, even if there are none
return $errors;
}
add_filter( 'registration_errors', 'so_32767928_blacklisted_user', 10, 3 );