fix email reply to issue (#326)

* fix email reply to issue

* fix: email  test  issue

* fix: phpunit  file

* style: fix lint

app/Mail/Forms/SubmissionConfirmationMail.php

@@ -63,6 +63,9 @@ class SubmissionConfirmationMail extends OpenFormMail implements ShouldQueue
     {
         $replyTo = Arr::get((array) $this->event->form->notification_settings, 'confirmation_reply_to', null);
 
-        return $replyTo ?? $default;
+        if ($replyTo && filter_var($replyTo, FILTER_VALIDATE_EMAIL)) {
+            return $replyTo;
+        }
+        return $default;
     }
 }