Create emails and inbox feature with PHP

When user finishes registering the php code should be able to create an email account for him/her. There should be an inbox feature as well.

For example John registers an user. He is created an email john@example.com. When someone sends email to this address John will receive those e-mails to the application inbox.

My server is not running cPanel or DirectAdmin.

What's the best way of doing it in the centOS7 server?