Validate email really exists

Just tonight I was having a look at hosting websites and I noticed one did exactly that. Normally I start plodding through registrations systems with nonsense like Name: asdfasdfasdf Email:asdfasd@asdf.co.uk etc etc but this one site knew it was a nonsense email. In the end I made up one that was almost certainly taken by someone and it passed but the process was really impressive, and I thought at the time - how do they do that?

I do not want to advertise the site but I think it was on: "e h o s t . c o m" - an example of a really impressive sign up process.

I just googled it and mailgun.com looks really good, does anyone know of any others, or has anyone used anything like this before?

PS Thinking about it, it is not as useful as I thought it might be (certainly for spam protection it is) but still have to validate ownership of the email for registration so still have to send an email for verification.