Hello @dyin , the answer from @fierevere is pretty solid. WordPress uses only PHP’s mail() function by default, however, you may go ahead and integrate it with dozens of other email services.
For example, a popular plugin such as WP Mail SMTP by WPForms can help you send your emails through Gmail, Sendinblue, Mailgun, Zoho, or other services. In fact, I have myself installed in on a couple of high-traffic WooCoomerce websites that send all their order notifications through Sendinblue and it works like charm.
Let us know if that is good enough for you!