style(rubocop): Style/ClassAndModuleChildren

config/initializers/smtp_extensions.rb

@@ -1,14 +1,7 @@
 # frozen_string_literal: true
 
-class Net::SMTP::Response
-
-  def message
-    @string
-  end
-
-end
-
-class Net::SMTP
+module Net
+  class SMTP
 
     attr_accessor :source_address
 
@@ -37,4 +30,13 @@ class Net::SMTP
       TCPSocket.open(address, port, source_address)
     end
 
+    class Response
+
+      def message
+        @string
+      end
+
+    end
+
+  end
 end