Lync mobile clients connect through the external web services connection, which should be published on port 443 TCP. This requirement should be fairly standard and should be implemented with all Lync deployments involving external users. Apple iOS devices that are connected to the internal infrastructure will require a unique firewall rule for push notification connectivity. When an Apple iOS device attempts to connect to the Apple Push Notification Service, the device initiates an outbound connection on port 5223 TCP. It is important to ensure that this connectivity is allowed outbound from the corporate network for these devices to functional properly.