That was my misunderstanding. I thought with the hardware and settings mentioned above, I would be able to read the data from any Technoline sensor. There's a YouTube video from Miika Kurkela explaining how to interpret the data from these sensors. But to be honest, I only unterstand half of it.

@Yveaux: thanks for the information. I thought it's much easier. I heard about LaCrosse Gateway which seems to be able to connect to Technoline temperature and humidity sensors with Nodemcu and RFM69 hardware and connect it to FHEM. I wanted to have a more general approach and just forward data from technoline sensors via MQTT. But if this is a totally different protocol I'll have to look for another solution.

My first post at mysensors.org. Sounds like a great tool. Tried to set up an MQTT Gateway with Hardware as described above, ESP8266 and RFM69W with 868 MHz, to connect some Technoline TX29DTH-IT temperature and humidity sensors, without success. ES8266 is working , connects with my wifi network and also connects to my mosquitto server. But I do not get any connection from RFM to technoline. Is there anyone out there who was able to get this running?