I recently located a very easy way to validate emails on the CTA form with one small piece of java script code using a very cost effective (almost free) service. Here is the instruction page on how to implement email validation using Neverbounce:

https://neverbounce.com/integrations/unbounce

I found that I had to add it at the page level versus at the domain level using the script manager. We got tired of paying for ads to our landing pages and have some mistype their email address on the few forms where we do not require a phone number.