Email Validation: Why and How to Do It?

Old article but really actual in this time

https://proofy.io/email-validation-why-and-how-to-do-it/
"We talk about email validation, the reasons why it is required and how it works, and we talk about how to check the presence of the domain and IP in the spam lists as well as what to do if they are already there."
Please read and give feedback.
thank you