We've often heard concerns from clients about validating emails submitted the Justuno promotions, especially if that client wants to give the visitor a coupon code on the spot and send them on their way. To solve this, we have now integrated with BriteVerify, a software that can verify email addresses instantly, and even lets you accept specific types of email addresses (unknown. role addresses, to name a few). Not only can you collect clean emails, but you can do so while presenting a coupon code to check out in that same session.
You must have a BriteVerify account in order to use this integration. Once you do, you can access this in the design canvas by clicking on the email field, then clicking the button on the right that says Email Verification.
Here's a gif to illustrate the point:
You can find further support documentation here. Enjoy!