1 files changed, 17 insertions, 2 deletions
diff --git a/actionmailer/lib/rails/generators/mailer/mailer_generator.rb b/actionmailer/lib/rails/generators/mailer/mailer_generator.rb
index 5a5c9d32bb..9dd7ee7a27 100644
--- a/actionmailer/lib/rails/generators/mailer/mailer_generator.rb
+++ b/actionmailer/lib/rails/generators/mailer/mailer_generator.rb
@@ -8,14 +8,29 @@ module Rails
       check_class_collision suffix: "Mailer"
 
       def create_mailer_file
-        template "mailer.rb", File.join('app/mailers', class_path, "#{file_name}_mailer.rb")
+        template "mailer.rb", File.join("app/mailers", class_path, "#{file_name}_mailer.rb")
+
+        in_root do
+          if self.behavior == :invoke && !File.exist?(application_mailer_file_name)
+            template "application_mailer.rb", application_mailer_file_name
+          end
+        end
       end
 
       hook_for :template_engine, :test_framework
 
       protected
         def file_name
-          @_file_name ||= super.gsub(/\_mailer/i, '')
+          @_file_name ||= super.gsub(/_mailer/i, "")
+        end
+
+      private
+        def application_mailer_file_name
+          @_application_mailer_file_name ||= if mountable_engine?
+            "app/mailers/#{namespaced_path}/application_mailer.rb"
+          else
+            "app/mailers/application_mailer.rb"
+          end
         end
     end
   end