Nextcloud Mail App does not work as it should

Hey, I have my nextcloud running in a docker container on my ubuntu vm and its working fine so far, but recently I wanted to intigrate my icloud mail account (which I also use to receive admin notifications).
The app seems to work and I have my mail account properly connected, but I can’t see any received mail. I can however send mails and I can see the number of unread mails in the app.
my problem is that i can’t see my new mails as if my nc doesn’t have permission to view them, so i can only see the number of new mails but not the content.

App version is 2.2.2
NC version 25.0.3