So it seems that (for now at least) a campaign must have the FROM address as the app mail address. At least the same actual address, but the "friendly name" can be changed. Which is good.
Good points. So, if you let Cloudron manage the email address, then you have to change it from Cloudron Dashboard -> App -> Email -> From address setting. This will fixup the config accordingly. You can also change the setting there to have Cloudron not manage the email at all (if you want to relay using some other provider from inside listmonk).
The name is not configurable but it should be, will fix the package (or the box code).