The Digital Preservation Coalition has released Preserving Email.
Here's an excerpt from the announcement:
Gareth Knight of King's College London welcomed the report. 'Preserving Email provides an excellent overview of the topic, drawing together observations made in a number of research projects to provide a succinct overview of the legal, technical, and cultural issues that must be addressed to ensure that these digital assets can be curated and preserved in the long-term. Its conclusion, providing a set of pragmatic, easy-to-understand recommendations that individuals and institutions may apply to better manage their email archive, highlights the complexity of email preservation. It also sends a clear message that it is something that everyone can perform.'