Why/How does an email address get added to the bounce list?

I know how to remove an email address from the bounce list, but am unclear how or why it gets added to the list in the first place. Also, is there a way to be alerted that an email address that previously worked has been added to the list? Thank you!

There are several reasons why your email address may have been added to the bounce list. It could be due to a non-existent/inactive email address, your mail server being unavailable, your mailbox is full or JotForm is on your blacklist. JotForm will stop sending emails when your email address is in the bounce list. Please note that high bounce rates will put our sending method at risk so we have to process the bounce messages without exceptions.

I would suggest you to set up your email notifications according to this guide:

https://www.jotform.com/help/208-How-to-setup-email-alerts-to-prevent-email-bouncing-related-issues 

Also you can contact your email provider and request them to Whitelist JotMails IP Addresses.

It is not possible to be alerted if email address is added to bounce list.

Hope this will help. Let us know if you need further assistance.