Methods and systems are described for resolving a first node identifier in a first identifier domain space to a second node identifier in a second identifier domain space. In one aspect, a first node identifier from a first identifier domain space is identified. The first node identifier is included in data for transmission to a recipient. A network directory service node address is determined for a network directory service node configured to resolve the first node identifier to a second node identifier in a second identifier domain space. A message including the data and addressed to the recipient is generated. The message is transmitted to the recipient in association with transmitting, to the recipient, the network directory service node address.