I run my own little matrix synapse homeserver, to offer some services for the family and friends.
With the move from beta 0.9x to final 1.0 the synapse server setup required some serious changes to the hosting that I failed to apply at that time and lost federation and with that the possibility to chat with "foreigners".
Finally, I took another go at the issue and here we are: federation working!
Still, with Nginx alone, I was not able to accomplish the required serving of the
stuff. But since I had introduced Traefik already on the server for other purposes, this finally lead the way to success:
Traefik => Synapse directly (previously this was handled by nginx)
Traefik => Nginx for serving the .wellk-nown stuff (this did not work when nginx was the proxy for synapse)