Add mail headers to avoid auto-replies (#23597)

app/mailers/application_mailer.rb

@@ -7,6 +7,8 @@ class ApplicationMailer < ActionMailer::Base
   helper :instance
   helper :formatting
 
+  after_action :set_autoreply_headers!
+
   protected
 
   def locale_for_account(account)
@@ -14,4 +16,10 @@ class ApplicationMailer < ActionMailer::Base
       yield
     end
   end
+
+  def set_autoreply_headers!
+    headers['Precedence'] = 'list'
+    headers['X-Auto-Response-Suppress'] = 'All'
+    headers['Auto-Submitted'] = 'auto-generated'
+  end
 end