Hey Armin, thank you very much!!!
Thanks for the infos and super good that you can fix the problem here : )
"then i realized this setting is not compatible with lay theme, i fixed that too on your website. this will be included with the next update"
The e-mail is working. Problem was that the system blocks links with .../wp-admin as spam directly ;( sorry!
(And the site is still under construction and a test to see whether the plug-ins all work as desired. The links and content are not yet finalised.)
Thanks and best!!!