Examples described herein include systems and methods for controlling access to a server, such as an email server or a gateway, in situations where the identity of the requesting device is unknown or where the user device accesses the server using an unknown or unmanaged application. In one example, the system can utilize a user authentication credential included in the request to identify other devices belonging to the user that happen to be enrolled with the system. An out-of-band message can be sent to those enrolled devices, requesting confirmation from the user and, in conjunction with an authentication token, allowing the system to trust the previously unknown device. In the example of an unmanaged application attempting to access an email server, the system can confirm compliance of the requesting device and issue an authentication token that, along with an appropriate command sent to the email server, provides access.