If you are unable to validate via email, you can also validate using DNS.
However, we strongly advise you to have an active website behind your domain name as this will help with email deliverability.
But how reliable is validating emails domain (does it exists at all) by reverse dns. I don't care in this part is it some spam address or not, I just want to know if domain exists at all and is able to receive and send emails. I want to validate emails domain name, if it exists.
I've asked similar question on board for programmers, but I can't get full answer, so I think this board will be better for such question.
The DNS records like MX, CNAME are returned by your Name Servers and are available with your DNS Host.
You can get the help of your DNS Registrar/ DNS host to get assistance in this.