If you want it in the system tray I think what you'll have to do is make it a Windows service. I've only written 1 Windows Service and that was years ago, but I believe that's what you'll have to do.
If I'm correct about writing a Windows service, then what I would suggest you do is create a new Visual Studio solution and add two projects to it. One would be a DLL which would run as a Windows service. The second project would be a WPF project that will be your UI the user interacts with. Then you'll have to use some messaging system to communicate between the two.
For the action messages that would mimic what Outlook does, I've used some WPF toast messages to accomplish that. If you Bing/Google "WPF toast popup" you'll get lots of results.
I hope this helps.