Abstract: In one embodiment, device presence enables persistent access to a set of resources, which may be data or services. Unique device identifiers are assigned to different computers of a user to identify the computers of the user of a network. For example, a device identifier is specific for a user and specific for a messaging system. Some time-consuming and device-specific tasks, such as synchronization of photo albums, transmitting files, sharing a printer, etc., may be interrupted temporarily, such as when the computer is restarted. Using the device identifiers, the messaging system can uniquely identify the devices involved in the tasks and detect the presence of the devices so that, after the interruption, the tasks can be resumed without user intervention.