A method for creating an index of network data for a set of message data, the index being arranged for searching the set of message data. A method in accordance with an embodiment of the invention includes: creating a set of dialogue records, where each the dialogue record is the set of messages corresponding to a dialogue between a sender and recipient pair in a message corpus; —logging each of the set of messages in each corresponding dialogue record; and creating an index of terms from the set of messages, the index being arranged to index each term to each dialogue record in which the message comprising the respective term is logged.