Many knowledge management (KM) systems have proven unsustainable to date, exhibiting low quantities and quality of knowledge, with systems falling into disuse. In this paper, we provide and explore a model for sustainable KM systems, focusing on the advantages to be gained from integrating knowledge work with everyday work practices, and enabling sensemaking through personalisation and contextualisation. We employ a discourse analysis of email as an exemplar of a sustainable KM system, thereby identifying a number of key characteristics for sustainable KM systems. Our model for sustainable KM systems adds to existing KM theory and, more immediately, assists companies by providing an understanding of the kinds of characteristics likely to make KM systems more effective, and sustainable in the long term.