Hi Andreas,
Sorry for the trouble. We are not purposefully trying to launch Outlook - I would not wish that on anyone! I have seen a similar issue on some Windows machines in the past, where either the default mail program, such as Outlook, or web browser, or sometimes the system Calculator would be launched, possibly in the background, but that might prompt the user to sign-in or set up the mail/browser system. When I looked into this (now ~5 years ago), I could get this to happen and narrowed it down to certain wxPython components, but ones that we do use regularly.
Slightly "in the weeds": At the suggestion of wxPython developers, I added a wrapper around Python opening a process or doing the equivalent of a Windows "Start" command that would print out a message before doing such a "start". In a classic debugging story, adding that wrapper never showed the actual problem, but also made the problem appear to go away. I have not seen this bug in years. About a year ago, I was doing some "cleanup" and removed this wrapper. I have not seen or heard of the problem since. But, I will add this back. With that back in place, if you (or anyone else) sees this happen, please look at the Windows cmd shell for any messages that might show up and let me know.
I'm hoping to tag and push 0.9.69 out to PyPI today or early tomorrow, and this will be included. FWIW, 0.9.69 will be a "beta"-like pre-release and not yet pushed out as an automatic update, and a more official release of 0.9.70 probably by next Monday. In fact, one of the problems to solve is the failure of automatic updates on Windows. I'll send out more complete announcements for both of these.