What is Bounce List in the Account Settings?

That's for checking if your email address is listed as bounce email to our server.

When our system sends the form emails to your email address, and the delivery fails, we will mark the emails as old or rejected or expired, and we will move to add the email address to our bounce list. 

The delivery fails when you have active anti-spam measures that block Jotform or your hosting provider detects us an unknown sender and proceed to block us. There are also cases that when the recipient's inbox is full, and will not be able to receive our emails.

The guide below will help you prevent it:

https://www.jotform.com/help/208-How-to-Prevent-Email-Bouncing-Related-Issues 

I hope that helps. Please let us know if you need more information regarding this matter.