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.
That is probably because of your current form settings or could be because of the settings of the recipient email, not accepting emails for senders that are not on the contact list. Please let us know what form so we can check your settings.
Also, check this related guide: http://www.jotform.com/help/208-How-to-setup-email-alerts-to-prevent-email-bouncing-related-issues.