Well unless you enter the product key for your exchange server it is considered to be a trial edition
Exchange 2016 trial is valid for 180 Days after that trail expires.
So lets see how to enter the product key
Note: you will have to restart information store service on exchange server after you enter the key.
you can use the below command to enter the product key for the exchange.
Set-ExchangeServer ExServer01 -ProductKey XXXXX-XXXXX-XXXXX-XXXXX-XXXXX