Your product key is to verify that you’ve purchased an Exchange Server Standard or Enterprise Edition license. If you don’t have a product key or don’t enter one, your server is automatically licensed as a Standard trial edition. The trial will only be good for 180 days, after that, you will need to purchase a product key. 

Before you begin

• To open the EAC, see Exchange admin center in Exchange Server. To open the Exchange Management Shell, see Open the Exchange Management Shell.
• You need to be assigned permissions before you can perform this procedure.
• After you license an Exchange Mailbox server, you need to restart the Microsoft Exchange Information Store service on the server after you enter the product key.
• You can upgrade from a Standard Edition license to an Enterprise Edition license. You can't downgrade from an Enterprise Edition license to a Standard Edition license without reinstalling Exchange.

Use the EAC to enter the product key

1. In the EAC. go to Servers > Servers, select the server you want to license, and then do either of the following steps:
1. Click Edit Edit icon.
2. In the details pane, click Enter Product Key.
2. The Exchange server properties window opens. On the General tab, do one of the following steps:
1. License an unlicensed server: Enter the product key in the Enter a valid product key text boxes.
2. Change or upgrade the product key on a licensed server: Select Change product key and enter the product key in the Enter a valid product key text boxes.

After you have finished this step, click Save.

After you license a Mailbox server, do the following steps to restart the Microsoft Exchange Information Store service:

• On the Exchange server, open the Windows Services console.
• Run the command services.msc from the Run dialog, a Command Prompt window, or the Exchange Management Shell.
• Open Server Manager, and then click Tools > Services.
• In the list of services, right-click on Microsoft Exchange Information Store, and then click Restart.

Use the Exchange Management Shell to enter the product key

1. To enter the product key in the Exchange Management Shell, use this syntax:
1. Set-ExchangeServer <ServerName> -ProductKey <ProductKey>
2. After you license a Mailbox server, run the following command in the Exchange Management Shell to restart the Microsoft Exchange Information Store service:
1. Restart-Service MSExchangeIS

Verify it worked

To verify that you've successfully licensed the Exchange server, do any of the following steps:

• In the EAC, go to Servers > Servers, and select the server you licensed. In the details pane, verify the Exchange edition value (Standard or Enterprise) and whether the value Licensed is present.

• In the Exchange Management Shell, replace <ServerName> with the name of the Exchange server you licensed, and run the following command to verify the property values:

• Get-ExchangeServer <ServerName> | Format-List Name,Edition,*Trial*

• In the Exchange Management Shell, run the following command to view the licensing status of all Exchange servers in your organization:

• Get-ExchangeServer | Format-Table -Auto Name,Edition,*Trial*