I'm trying to make a modeless window that will open the mails of a
specific message class. The problem is, that GroupWise traps some
keyboard events that will never make it to my modeless window. So far
I'm using modal windows, but that's an issue.

I read this in the c3po documentation:
"Modeless dialog boxes are best implemented in an out-of-process server.
Because GroupWise traps keyboard events (to turn them into accelerators
and eventually into tokens), a .DLL server will experience problems
receiving keyboard events when creating a modeless dialog box or window."

So, the question is, how do I do that in C#?