diff -u b/reroute_email.module b/reroute_email.module
--- b/reroute_email.module
+++ b/reroute_email.module
@@ -8,7 +8,6 @@
 use Drupal\Core\StringTranslation\TranslatableMarkup;
 use Egulias\EmailValidator\EmailParser;
 use Egulias\EmailValidator\EmailLexer;
-use Drupal\Component\Utility\Unicode;
 
 define('REROUTE_EMAIL_ENABLE', 'enable');
 define('REROUTE_EMAIL_ADDRESS', 'address');
@@ -231,7 +230,7 @@
       // The part after the @ sign is the domain and according to RFC 1035,
       // section 3.1: "Name servers and resolvers must compare [domains] in a
       // case-insensitive manner".
-      $domain = Unicode::mb_strtolower($matches[1]);
+      $domain = mb_strtolower($matches[1]);
 
       $whitelisted_domains[$domain] = $domain;
       unset($whitelisted_addresses[$key]);
@@ -249,7 +248,7 @@
     }
 
     // Check whitelisted emails and domains.
-    $domain = Unicode::mb_strtolower((new EmailParser(new EmailLexer()))->parse($email)['domain']);
+    $domain = mb_strtolower((new EmailParser(new EmailLexer()))->parse($email)['domain']);
     if (in_array($email, $whitelisted_addresses, TRUE) ||
       in_array($domain, $whitelisted_domains, TRUE)) {
       continue;