Is there ever a bottle-neck where if to much traffic or volume that will cause the email notification to fail?

Is there ever a bottle-neck where if to much traffic or volume that will cause the email notification to fail other then a user putting in an incorrect email address or the format is not correct? 

Traffic won't be an issue as mentioned on your first thread. The only thing you need to worry about is the Form Views limit per plan. And on the Free Plan, you're limited to 1000 Form Views per month.

You specifically mentioned "other then a user putting in an incorrect email address or the format is not correct" so I'm assuming you're talking about Autoresponders. If you have a form that is not sending out Autoresponders, give us the Form ID/URL so we can have a closer look.