I know freepbx supports let’s encrypt but seeing my server is not connected directly to the internet (and also no portforwarding) I was wondering if it’s possible to use let’s encrypt with dns challenge.
No. The initial setup and all renewals require port 80
or 443 access from the LetsEncrypt servers to your PBX.
Too bad. Maybe something to look at? Consider it a feature request
Not how we do that - if you want to request a feature, submit a feature request through the issues tab…