If you like, you can send us an email to info@soscisurvey.de with the email address you have tested with. We can then check that the email logs says.
Usually they tell me that the email was send to the mailserver that's responsible for the email address, and it got lost afterwards. And then you'll have to contact the company running that mailserver, and probably it turns out that some spamfilter removed the email and did not notify the person.