If any users or queues in your organization are not using Microsoft Dynamics CRM for Outlook to send and receive e-mail messages for Microsoft Dynamics CRM, you must install Microsoft Dynamics CRM E-mail Router, and then configure the individual user records.
Important
Only one instance of the E-mail Router should be installed in an organization.
More information: Determining E-mail Access for Your Organization
Install Microsoft Dynamics CRM E-mail Router
Set the option to send and receive e-mail from a user or queue