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.
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This still isn't working!!!
We're sending out the form emails to the recipients of the form in this question. You can check that in your account by following the steps from this guide: http://www.jotform.com/help/293-How-to-view-all-your-form-Email-History.
Now, since we're sending out the emails just fine, I think you should check this problem with your hosting provider to see whether they allow SENDMAIL method since this is what we used for custom sender emails.
You may also need to add us to your server whitelist: http://www.jotform.com/help/145-Whitelisting-JotMails-IP-Addresses.
Lastly, if the verified custom sender email is not working after adding us to your server whitelist, I would suggest using SMTP method instead. We have two methods:
SMTP from your hosting provider: http://www.jotform.com/help/244-How-to-Setup-SMTP-for-a-Form.
All of the above links are excerpt from this guide: