Version: (using KDE 4.3.0) Installed from: Compiled From Sources The behaviour of "Show KMail tray icon when there are unread messages" has changed between KDE 3.5.9 and KDE 4.3.0. In KDE3 when this option was selected, clicking on close button of KMail window resulted in window simply being hidden -- KMail stayed active and showed a tray icon _only_ when new mail was received. In KDE4 KMail simply exits when a close button is clicked. If I set "Always show KMail in the tray", clicking on close button hides the main window like in KDE3, but the annoying tray icon is always shown, regardless of presence of new mail. Please restore KDE3 behaviour.
This is by design, otherwise it is not possible to quit KMail if no new mail arrives. See also: http://www.intevation.de/roundup/kolab/issue3605