Hello Sebastian,
I set up 2 new email accounts for my website and then subscribed to my Newsletter on my site https://SillyGoatsSoap.com. i received a notice that I had to new subscribers to the newsletter…When I checked the 2 new email accounts there is no newsletter. It did not send.
I went into the control panel and manually added a subscriber and that did add that subscriber email.
Hope this helps and sorry it took so long to return reply but it did not notify me you commented back. I will watch more closely today.
Chris