Version: (using KDE Devel) Installed from: Compiled sources When managing accounts both receiving and sending accounts, the remove button is right between the other buttons and very easy to press. While you can undo the damage by quickly canceling all the configuration, doing so is not the most intuitive thing to do. I consider it a serious design mistake in the interface. It could be solved by moving the remove button to be in the buttom of the button panel away from the other buttons. Possible adding an icon or painting it red.
I think painting it red is a bad idea, since color blind people will not pick up on it, but moving it around a bit makes sense, I will take this up with the usability experts at the PIM meeting end of May
In kde 4 (4.3.0 actually) the dialog also has a "Reset" button that undo all the modifications since the dialog was opened or the Apply button was pressed. Therefore, a sending/receive account deleted by mistake can easily be restored.