Hi @Simon55
this has been discussed already here
Buffering messages with connection lost on thin-edge.io and here
Cumulocity Device with inconsistent internet access
In short: Yes, thin-edge.io buffers the messages using the local mosquitto broker. When persistence is enabled it is written to disk and when at least QoS 1 is sent the messages are forwarded to Cumulocity when the connection is restored.
Extra answer: It is the most straight forward way yes and by far the best maintained open-source project, but of course there are multiple other so called “agents”. Some of them are pretty old or not much maintained but could be a start.
Have a look here: https://open-source.softwareag.com/cumulocity-os-repo-overview/#agents