I'm running (a program which calls a program which calls) “kde-open5 mailto:e@mail.address”. This starts up kmail. I would prefer a different mail client, so I changed the system settings Programs→Default programs→E-mail client. But kde-open5 still tries to start kmail. How can I tell it to run my preferred agent instead? What settings does it look at?

OS: Fedora 32
kde-cli-tools-5.18.5-1.fc32.x86_64
plasma-systemsettings-5.18.3-1.fc32.x86_64