Automatic Delivery Status Notification with Thunderbird

Thunderbird has an option to request for a Delivery Status Notification. But you have to check that option for every single mail.
If you want it automated you have to change some settings that are not in the regular menus.
Goto :
Edit -> Preferences -> Advanced -> General -> Config Editor.
Now you get a warning :

Click “I accept the risk!”
You have to make 2 changes :
mail.dsn.always_request_on false
mail.identity.default.use_custom_prefs false

Change them to :
mail.dsn.always_request_on true
mail.identity.default.use_custom_prefs true