I recently started a new project on CodePlex called Controlled Vocabulary. If you are the admin of an email group alias then you may find it useful to distribute to your members. The driving motivation behind this project is that Controlled Vocabulary is a more effective method of categorizing emails than an open tagging system, which is too subjective. The project provides various tools to support the adoption of a Controlled Vocabulary, e.g. Outlook Add-ins.
There is full documentation on the site to guide you through configuring your Outlook Add-ins. Please take a look and let me know if you find it useful or have any issue.