Thanks for your answers @luxflow,
anyone can access your seafile regardless of your listening port(80,81..82)
I'm not quite sure if I understand you correctly. I have a public IP, yes. My ISP doesn't block my port 80. At the moment my router is set to forward incoming requests on port 80 to port 80 of my omv-installation. And I assume that's the prerequisit for getting a valid lets-encrypt certificate. But if I disable this port-forwarding-rule no one can access my server. At least that's my understanding.
And currently this is also my problem. Because omv is also running on port 80 I am now able to access my omv-installation via internet, which is what I want to disable!
why are you blocking 80 port?
I am not blocking port 80, at the moment it is open. It's just that I don't want my omv to be reachable via internet, i.e. I would disable the port forwarding to port 80 completely, but then I couldn't certificate (once each 3 months).
if I were you, I only open /.well-know/acme-challenge for 80 port
and make anything else redirect to 443(https)
That's what my plan is, and I actually have already set the servers in nginx plugin this way (see my first post, the two spoilers).
Ok, so right now seafile isn't installed at all, but the server-settings in the plugin are already activated. If I now go to xxx.mydomain.tld I land on my omv login screen. That's what I don't want. So, the only way that came into my mind, was to change the port of omv, so that it isn't running on port 80 anymore.
I hope you guys get what I want.
Thanks a lot for your help.