In distributed agile teams, people often use email as a knowledge sharing tool to clarify the project requirements (aka user stories). Knowledge about the project included in these emails is easily lost when recipients leave the project or delete emails for various reasons. However, the knowledge contained in the emails may be needed for useful purposes such as re-engineering software, changing vendor and so on. But, it is difficult to relate texts such as emails to certain topics because the relation is not explicit. In this paper, we present and evaluate a technique for automatically relating emails with user stories based on their text and context similarity. Agile project management tools can use this technique to automatically build a knowledge base that is otherwise costly to produce and maintain.