Add email blacklist check to prevent sending to specific addresses

- Added a static blacklist in `sendEmailMailerSend` to skip sending emails to blacklisted addresses.
- Implemented a return condition if the recipient email matches the blacklist.

services/nginx/app/classes/email.php

@@ -120,6 +120,14 @@ class email implements email_i
      */
     private function sendEmailMailerSend(string $to, string $recipient_name, string $subject, string $message, string $html = null, string $references = null, array $attachments = []): void
     {
+        // Check if the email is blacklisted
+        $blacklisted_emails = [
+            'invoice.dk@freja.com', // TODO: Make this dynamic.
+        ];
+        // If the email is blacklisted, return without sending the email
+        if (in_array($to, $blacklisted_emails)) {
+            return;
+        }
         // Send POST request to email service
         $mailersend = new MailerSend(['api_key' => $this->config->mailersend_api_key->getVariableValue()]);