Dear Eduan, thank you very much for answering, I really appreciate that! Maybe I didn´t find the right words to describe my problem (at least my first one). I will try to express myself a bit more briefly now.
1. I looked up my email configuration in the s2member-area again and tried to be more accurate, but still I cannot find an option, where new registered users get an email, in which they have to confirm the adress that they stated in the registration process. of course new users get a "thanks for registering"-email, but still they are free to type in any mail-adress they want, without having to validate it. in that email should be a link to click, to confirm the true mail-adress. without clicking that link, they shouldn´t be able to log in.
do you get my point?
2. I am using the non-pro-version, so thank you very much for your link!
Thank you very much again for caring!