The validation i have mentioned is a syntax based validation. i.e… it looks for the proper email format in the user response (with @ symbol and ending with a .xyz).
What you are referring to is email reachability check. That is something that can be done using the API integration feature, where you can send the email to a 3rd party API which does this email reachability check and tell you if the email is reachable or not.
The service you have mentioned seems to have an API to do this. However I would only suggest you to do this extra check, only if you are getting tons of traffic on your Bot and a significant part of that is Spam. This is not very common, specially if the bot is new and relatively unknown. So I wouldn’t worry about email reachability test unless it is an actual problem, rather than a theoretical one.