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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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Please be noted that submission emails and the auto-responders are sent almost instantly as soon as the form is submitted.
I am not sure what is causing the delay but it could be related to your server. I would suggest you to use your own email address to send submission emails instead of using "firstname.lastname@example.org. You should setup a custom "Sender E-mail" option. The following guide should help you:
Do try the custom sender option and see if this speeds up the time in receiving the submission emails.