Hi Ben,
Yes, I checked.
I installed OX in LXC Container in Proxmox.
Connection via Nginx Proxy Manager
Gui works with Mails from dovecot in UCS
DAV Connection not.
→ After hours I found out to install open-xchange-dav
OX-Connector not.
→ After Dirks info I installed the certificates.
Stil not working
– > After hours I found out to install open-xchange-admin-soap
Connection between OX and UCS works now. But Password are not sync. This I found out after …
In the end, it was Lucifer 
“What is it that you truly desire?”
And the answer is:
OX, Nextcloud and Samba.
So I stopped my UCS VM after nearly 10 Years
- Using OX on a LXC Container (including dovecot and exim4)
- Using Nextcloud on a LXC Container
- Using Samba in docker in same VM as Nginx Proxy manager
Bye Bye UCS
@BenSommer: Thank you to install OX nativ