diff --git a/app/controllers/action_mailbox/base_controller.rb b/app/controllers/action_mailbox/base_controller.rb
index c234ecd250..5af59f8140 100644
--- a/app/controllers/action_mailbox/base_controller.rb
+++ b/app/controllers/action_mailbox/base_controller.rb
@@ -1,3 +1,4 @@
+# The base class for all Active Mailbox ingress controllers.
 class ActionMailbox::BaseController < ActionController::Base
   skip_forgery_protection