A first computing system can receive a proximity message from a source device, the proximity message comprising a device identifier and a network address. The first computing system can further determine that the first computing system is within a particular distance of the source device based, at least in part, on the proximity message. In response, the first computing system can send a proximity notification to a second computing system. The proximity notification can comprise the device identifier and a user identifier. The second computing system can receive the proximity notification. The second computing system can further determine user metadata associated with the user identifier. The second computing system can further determine a third computing system based, at least in part, on a mapping between the device identifier and a computing system identifier. The second computing system can further send the user metadata to the third computing system.