Since a while I’m not able to go to this this forum directly from the bookmark in my browser. I get a message:
Cannot load app
It looks like you are offline! Please check your network connection and try again.
I’m not offline and when I first visit https://mailinabox.email/ and from there select “discussion forum” under the quick links it works.
When I switch off the IPv6 stack on my PC the bookmark for the forum works too, so I recon there is something amiss with the IPv6 configuration on the server that runs the forum.
No showstopper, but a minor nuisance.