You can achieve exactly this by reading and replying your Outlookmail through Zoot (www.zootsoftware.com). Zoot synchronizes from and to Outlook on the fly, so you can mail either from Zoot or from Outlook.
Zoot is a PIM, probably known, with many swiss knife like functions. In Zoot you can have autosorting, assignments to words, categories, etc.
BTW, thanks for another fine article.
- Thees Peereboom