— Actually, the protocols support asking the mailserver
— So you can with reasonable accuracy do it
— But the question is; why not just send an email?
— Sendgrid is free ?
— No; it has a free month limit, but in production it will not enough. So it’s not free.
— If i send thru gmail, can we know the result ?
— I think not. But I’m not actually sure.
— If you are gonna use the Google GMail API you have to know that is very limited for a normal gmail account. And you have to pay a GSuit account if your plans include to launch something to production. It’s not the approach I would choose. The other thing you can do to validate an email and check if the recipient is the actual user is to actually send a email with a link and a message with the reason of the link, advertising that if he/she didn’t request that link is better not to open.