JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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 is indeed possible to limit submissions to one per email address. While editing your form, click on the preferences button. From that menu, click on the advanced tab:
Change the Unique Question to your email field to set it as the unique question. Click on "Save Changes" to complete the process.
thanks for the reply.
how can I modify this message (in italian) when multiple submissions are disabled for this form
You can modify any warning settings from the PREFERENCE settings
In the GENERAL tab, press the ADD button next to the FORM WARNINGS. This will open a new window will all the warnings Jotform contains. Just search and click over the warning you wish to modify.