Well after switching to KDE, I installed my favorite email application Mozilla Thunderbird, everything worked except I wasn't able to minimize it in system tray. In GNOME I was using New Mail Icon add-on and it was working fine, I was able to minimize it to the GNOME system tray but in KDE4.2 it is not working and I believe that this add-on is written specifically for either GNOME or KDE 3 (that I didn't test)
I was struggling for a day and then I found a way in KDE that can keep any application in system tray, which is super cool because I'm not dependent on add-on or any other extension. Follow the steps to start Thunderbird or any other application to sit in KDE system tray
- Start Yast and search for the "Alltray" utility and install it
- Right Click on the "Kick Off Application Launcher"
- Select Menu editor
- Go to Internet->Mail->Thunderbird
- On the right hand side in "General" tab you'll find "Command" which will have the command "thunderbird"
- Replace the command with the "alltray -s -l thunderbird %u"
You'll see the Thunderbird in the system tray. I hope this will help many people like me who want some applications to be available in system tray.