Show which domains were used in the spam_post_blocked notification

config/locales/server.en.yml

@@ -949,6 +949,8 @@ en:
       text_body_template: |
         This is an automated message to inform you that the new user [%{username}](%{user_url}) tried to create multiple posts with links to the same domain, but they were blocked based on the newuser_spam_host_threshold site setting.
 
+        Domain(s) included in %{username}'s posts: %{domains}
+
         Please [review the user](%{user_url}).
 
     unblocked:

lib/post_creator.rb

@@ -75,7 +75,11 @@ class PostCreator
     end
 
     if @spam
-      GroupMessage.create( Group[:moderators].name, :spam_post_blocked, {user: @user, limit_once_per: 24.hours} )
+      GroupMessage.create( Group[:moderators].name,
+                           :spam_post_blocked,
+                           { user: @user,
+                             limit_once_per: 24.hours,
+                             message_params: {domains: @post.linked_hosts.keys.join(', ')} } )
     end
 
     enqueue_jobs