Email not send after clicking "send"

I have tested the form at the link provided, I got “Erfolgreich abgeschickt ! Danke !” – which indicates that the form is sent.

However if you are not receiving emails, then they are probably being seen as spam somewhere in the email process. This is usually due to email headers (in particular the From email address used) or email content.

Emails can be considered spam for a whole host of reasons and get rejected at many points in the email process in addition to your spam folder.

See Contact Form 7 Email Issues – this links to a much more comprehensive article which also covers emails being considered spam.

See also Best Practice to Set Up Mail.