Ciao @bodo62,
Could you tell me what version of WordPress and Contact Form 7 you are using, so that I test with your environment? I gave it a try just now but after uninstalling the plugin (apart from removing the options) and the forms are in place, and I don’t see why this should happen.
> is there a way to be informed by email if a message ends up in spam ?
Currently not but I was thinking of doing a daily report in case spam was detected
> Can I disable the plugin completely?
to deactivate the plugin (the anti-spam function) you should remove the tick from all the antispam controls, whereas to deactivate the plugin completely you must do so from the wordpress plugins page