Exchange 2013 Messaging System (vii) Create a Send connector

First you need to enter the product key before you start configuring Exchange hosts

Exchange servers that do not have a product key entered can only use Standard Edition features. A maximum of 5 databases can be mounted per mailbox server. To complete the installation process, you need to enter a product key.

Enter Https://<casserver (FQDN) in the browser >/ECP open the EAC management console

Click Server, select the Exchange host you want to register, and then in the Action window on the right, click "Enter Product Key", open the Enter Product Key wizard, enter the legal product key for Exchange Server 2013, and click the "Save" button.

When completed, the Exchange host is registered as an Enterprise edition.