The first thing you should try is disabling Akonadi, the subsystem that sort of drives the kdepim (Kontact & co.) suite.
https://userbase.kde.org/Akonadi#Dis...nadi_subsystem
If that doesn't do the trick, open Kontact (the application that encompasses a bunch of related apps including Kmail) and find Configure Notifications in the Settings menu. Turn off all notifications for Kontact.
You can also right-click on your system tray and select System Tray Settings, and then select what entries you want to see and which you'd like to hide. Hide things like Korganizer and KMail and whatever else.
If stuff is still popping up here and there, go to System Settings (from your main application menu) and find the Startup and Shutdown category. Make sure that Kontact or KMail or kdepim-migrator (or whatever it might be called) isn't set to autostart upon login.
Finally, you could try removing kdepim to see if that suits. I'd be careful when doing that; I haven't tried it on Fedora in years, and I'm not sure what the dependencies are like now, so read carefully what is about to be removed before accepting (for instance, if removing kdepim also removes KDE, do not do it).