Icloud Mailbox does not work

Hi Community,
it’s me again. I’m in the middle of setting up my first Nextcloud. I have managed to overcome quite a few problems, but now I’m stuck on the next one. ICloud does not show me any Mails. I did set it up like I set it up with windows mail, where it works perfect fine using this manual.

But it gets weirder. Sending E-Mails with the Icloud Account works perfectly fine and When I get a new E-Mail it even says that there is a new Mail(1 next to the Mailbox) but I can’t see them. It just says “No messages in this mailbox”

I tried both IMAP usernames. Other E-Mail adresses from different provider work perfectly fine.

Nextcloud runs on an Ubuntu 22.04 Container in Proxmox.
Nextcloud Hub 4(26.0.1)
PHP 8.1.18

Thanks for help

I’m in the same situation with my iCloud email account: I can see there are unread emails but when I click on the inbox I get a “No messages in this mailbox” message. GMail works fine, instead.

Can anyone reply a tip or, better, a working solution?

Hi folks,
Maybe some of these might point to a solution?