Restrict MemberPress signups by a member's email address.

mepr-restrict-email-addresses.php

<?php

add_filter('mepr-validate-signup', function($errors) {
  /* Edit this to add or remove email addresses you'd like to block from registering.
     For example, if you'd like to block members with the following email addresses:
       - member@email.com
       - anothermember@google.com
     Then the code would look something like this: $email_addresses_to_block = ['member@email.com', 'anothermember@google.com'];
  */
  $email_addresses_to_block = ['member@email.com'];
  $user_email = isset($_POST['user_email']) ? trim($_POST['user_email']) : '';

  if(empty($user_email)) {
    return $errors;
  }

  if(in_array($user_email, $email_addresses_to_block)) {
    // Change 'Your email address is not allowed to sign up.' to the error message you'd like displayed
    // if the email address is blocked.
    $errors[] = 'Your email address is not allowed to sign up.';
  }

  return $errors;
});