use policies to protect sending email

app/policies/global_policy.rb

@@ -9,6 +9,7 @@ class GlobalPolicy < BasePolicy
       can! :log_in unless @user.access_locked?
       can! :access_api
       can! :access_git
+      can! :receive_notifications
     end
   end
 end

app/services/notification_service.rb

@@ -465,7 +465,7 @@ class NotificationService
     end
     users = users.to_a.compact.uniq
-    users = users.reject(&:blocked?)
+    users = users.select { |u| u.can?(:receive_notifications) }
     users.reject do |user|
       global_notification_setting = user.global_notification_setting