The Edge Server enables the users to communicate and collaborate with users outside the organization’s firewalls. These external users can include the organization’s own users who are currently working offsite, users from federated partner organizations, and outside users who have been invited to join conferences hosted on your Lync Server deployment. Edge Server also enables connectivity to public IM connectivity services, including Windows Live, AOL, and Yahoo!.

Edge Server Scalability

For performance, one physical Edge Server should be deployed for every 15,000 users that are expected to access a site remotely.