What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
It looks like your mail server rejected the emails coming form JotForm as provided by the error:Reason(s) : smtp; 554 5.1.0 Sender denied
You can try using firstname.lastname@example.org as your email sender.
If in case you still do not receive an email alert with using the said email above, you can try following step number 5 by contacting your email service provider and have the following IPs and domains whitelisted as provided in this link: https://www.jotform.com/help/145-Whitelisting-JotMails-IP-Addresses
In any case, please keep us posted.