suppress rejection email when email was sent to mailinglist mirror category

spec/fabricators/category_fabricator.rb

@@ -29,3 +29,9 @@ end
 Fabricator(:link_category, from: :category) do
   before_validation { |category, transients| category.topic_featured_link_allowed = true }
 end
+
+Fabricator(:mailinglist_mirror_category, from: :category) do
+  email_in 'list@example.com'
+  email_in_allow_strangers true
+  mailinglist_mirror true
+end