If you haven't checked this out yet, it is worth looking at.
Nathan Carlson, a developer on my team, created a VSTO Outlook Add-in that can read your mail using voice synthesis and also responds to voice commands.
You can download the source code here.
The sample demonstrates:
I had never known about the ability to create a custom action that could be used in Outlook rules--so it is worth checking out just to see how he does that.