Email is not receiving

No doubt in your spam box, as its html email.

ya it is html email. customer can receive new order mail. but seller cant receiving the new order mail.

They are sent using the same system – thats why I suggested spam. There are no known issues with emails not sending.

If customer shop in same day 2 times, then he/she won’t get second new order email. why? As well as Seller too won’t getting second email.

I suggest you implement email logging, because WC doesn’t limit sending.