1. A method to determine a user specific relevance score of a message, comprising: deriving, from correlations between the message and other messages within a message thread containing the message, a message model reflecting the correlations of the message with the other messages in the message thread, the messages being represented by accordingly linked nodes, wherein each node in the message model represents a corresponding one of the messages contained within the message thread and the sender and recipient of the corresponding message; and calculating, by a computer device, a numerical relevance score for the message, the calculation using a user specific ranking scheme and being based on the message model.