diff --git a/lib/email/sender.rb b/lib/email/sender.rb
index dbd0bdb983e..6ded4b88e9c 100644
--- a/lib/email/sender.rb
+++ b/lib/email/sender.rb
@@ -119,7 +119,7 @@ module Email
           # subcategory case
           if !topic.category.parent_category_id.nil?
             parent_category_name = Category.find_by(id: topic.category.parent_category_id).name
-            list_id = "#{SiteSetting.title} | #{topic.category.name} #{parent_category_name} <#{topic.category.name.downcase.tr(' ', '-')}.#{parent_category_name.downcase.tr(' ', '-')}.#{host}>"
+            list_id = "#{SiteSetting.title} | #{parent_category_name} #{topic.category.name} <#{topic.category.name.downcase.tr(' ', '-')}.#{parent_category_name.downcase.tr(' ', '-')}.#{host}>"
           end
         else
           list_id = "#{SiteSetting.title} <#{host}>"