JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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Are you referring to the notification emails of any of your JotForm? As I check your email history log, I didn't see any emails failed. I've checked some of the emails in our bounce list and they are not listed there as well.
If you are referring to any particular JotForm or email address, please let us know. We will be happy to investigate the issue further. Also, we request you to go through the guide below that can help you with troubleshooting email delivery issues.
Hope this information helps! Please get back to us if the issue still persists. We will be happy to assist you further.