To Fix Email send/receive problem.

1.I developed one website, regarding food delivery services just like food panda. 2. The problem happened recently.. when somebody out there register in website, admin/headquarter didn't receive any notification email about their registration 3. When somebody purchase the food, admin/headquarter also didn't receive any notification. 4. Sometime, admin receive notification/email coming-in, but only after several hours from order (delay in sending email). 5. sometime, yesterday's email (notification of new registration or new purchase, or new payment) received in bulk.. it should be on time without any delay. 6. Before this, when this thing happen, my effort is to update WP Mail plugin. And usually a bulk of email will coming-in. 7. But now even after keep on update, refresh, or clearing cache.. email unpredictably will receive. I sure there must be smarter way to fix this, rather than updating everyday. 8. Im using Wordpress + Food delivery themes, purchased from codecanyon. 9. Im using Google Gsuite to manage email 10. This totally devastating for my business. Anyone can help me to fix this?