How can I send everyone an email that signed up with my forms?

Unfortunately we do not have any option available to send email to all the users who submitted your form. Here are the options I would suggest you:

#1. You can export your submissions in Excel and then you can import the email addresses form Excel file in your email marketing or bulk email software to send submission emails. The following guide should help you how to export submission in Excel: https://www.jotform.com/help/73-How-to-Download-Form-Submissions-as-Excel-CSV-PDF

#2. You can also integrate your form with email marketing app as well but please note that this will only send new submissions to the integrated app. We have some email marketing and newsletter app integration: https://apps.jotform.com/category/emailling

Hope this helps.

Do get back to us if you have any questions.