Email doesn’t use port 443… it uses:
- 25 for SMTP (client or server)
- 465 for SMTP/SSL (client only)
- 587 for SMTP/TLS (client only)
If it says access from untrusted domain, that means the domain in the browser address bar isn’t among those in the config as trusted domains, or that a reverse proxy needs additional setup.
I wrote a guide for doing a Docker setup. Take a look.
https://help.nextcloud.com/t/howto-ubuntu-docker-nextcloud-talk-collabora/76430