New User registration email is not coming

Is any mail being sent from your site? Have you checked your spam folder, too, in case the problem is on the receiving end?

yes, for example, Thank you for contact us email is being sent to users. However, I am ot receiving new user registration email.

Can you receive any email from the site? Did you check your spam folder?

yes, I get the contact us email from users. nothing in spam folder

You might try using one of the SMTP plugins to send mail, as they offer error logging.

as a default, new registration email should come, right? in order to receive notification , do I need to upgrade non-free SMTP plugins?

They should come in due course. You do not need a non-free plugin.