>I want to determine the standard email client. How can I do this. The reason to find out which client is used is, that I want to use Outlook automation if it is Outlook, in the other case I want to use ShellExecute.

A better way to do this is with some MAPI ActiveX controls and a simple MAPI client (OE, OL, Exchange, doesn't really matter). Nigel Coates has a class to do it easily for you, and Doug Hennig wrote two articles on it just recently in FoxTalk.