Can I use an encryption service such as ProtonMail to send a notification email?

If you mean to use your ProtonMail as the sender email in the form, unfortunately, ProtonMail does not support IMAP, SMTP, and POP3 setup. You can read it here: 

https://protonmail.com/support/knowledge-base/imap-smtp-and-pop3-setup/ 

You may consider a non-protonmail email address to set up your own custom sender email.

https://www.jotform.com/help/244-How-to-Setup-SMTP-for-a-Form 

Thanks you for the quick response.

I have created a membership form which contains the name, dob and some medical history information template for the child of the person competing the form. While I am happy that both data entry via your https site and data storage is secure on your European servers are secure, I would like to forward this 'sensitive' data to the named 'manager' email address in the form. I don't believe I can do that securely by a notification email. I use yahoo as my email provider and have no control over the recipient email provider.

If you want to forward 'sensitive' data to the named 'manager' email address, but you do not want to use email Notification that contains all data, you can delete email Notification table and create report of your form submissions that is password protected and send it to the manager email address. 

How To Create Form Reports in Jotform

You can also encrypt your form. This way data will be encrypt on submission page of your form and inside of email Notification that is sent to the manager email address. You will also need to provide manager encryption key, so that he/she can decrypt the data. 

More about encrypted form you can find here:

Introducing Encrypted Forms: The Ultimate in Online Form Security

Encrypted Forms and How to Use Them

Please note that reports will not work if form is encrypted. 

Let us know if you need further assistance.