Here is a Microsoft documentation on this topic.
For your reference: Connect Microsoft Teams Essentials (AAD Identity) to an existing email system with calendar
While please kindly note that it may be very complicated.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.