Why does an address go to a bounce list?

One of our jotform email recipients is a distribution group, an gets delivered to 4 individuals. One of the users continually gets added to the bounce list, what causes an email address to be added to the bounce list? We changed to a distribution group as a troubleshooting step, as this has been happening to 3 of the recipients on a regular basis, and we have to log in and remove them from the list. I've also made sure jotform.com is an always allowed in their spam filter, and checked the mail settings on the client, no rules blocking the sender. 

There are many reasons regarding a bounce issue. However, the most common ones are that your e-mail provider rejects our e-mail or mark as spam. So, we try to send notification but you can not due to this rejection. 

We can say the exact reason if your e-mail is in bounce and not removed by you. You can check also either your e-mails in bounce or not by following steps here.  If you encounter bounce issue again, please contact us before remove and we can provide you the exact reason. 

On the other hand, if your e-mail keep constantly going to bounce, you can consider to use your own e-mail as sender by using your SMTP credential or you can whitelist our IP addresses. 

Related guides for both solutions :

1. SMTP 

2. Our IPs to be whitelisted.

ip4:64.247.128.0/18

ip4:129.121.0.0/16

ip4:152.160.0.0/16

ip4:65.75.128.0/18

ip4:209.126.119.0/20

If you have more questions, please feel free to contact us. We would be pleased to assist you for any issue you may have.