Dear Caimin,
Thanks for your rapid response!
I’m using Version 5.5.5. I did indeed try to change the Email Settings, but nether WP Mail, Qmail, Sendmail, PHP mail function, SMTP works. The strange thing is that everything work fine in the beginning, but after changing the default messages and trying to subscribe myself a few times (each time with a different mailadress), it stop working.
What could I have done wrong? How could I fix this?
Thanks