Why not set the default 'notification' to of the email choices. My guess is if someone has submitted a post/reply, they'd want to know if there were a reply. I prsonally forget there is a 'notification' checkbox at very bottom, and then have to go back to edit the post to turn on 'notification'.
Click on User CP look in Control Panel for and click on Edit Options Look in Messaging & Notification for Default Thread Subscription Mode When you post a new thread, or reply to a topic, you can choose to automatically add that thread to your list of subscribed threads, with the option to receive email notification of new replies to that thread. There is a drop down box that you can set your default to do that. You have a choice of Instant, Daily or Weekly notifications