Alternatively, formspree could publish a public key which you could use to encrypt your email address. To make it easy, they would just have a form on their web

Alternatively, formspree could publish a public key which you could use to encrypt your email address. To make it easy, they would just have a form on their website which does the encryption for you, giving you the opaque string to use in your form. The UX for the user is the same if Formspree were to just generate a random token and store in their DB mapping it to an email, but this way Formspree doesn't need to store anything in their DB.