A couple of weeks ago I tried to switch my E-Mail-Client from Thunderbird to KMail. I'm very content with the design and GUI, but there is still a fatal problem. When start KMail appears "KMail is loading is loading the content of the folder Please wait..." or so.
The only thing which helps for a short time is a restart of the Akonadi-Server.
Strange is the fact that there a no problems when I'm logged in a friend's network.
Has somebody a idea

What version of KDE PIM are you running?

I have Kontact 4.11.5.

Can you try disabling Desktop Search in System Settings and see if the situation improves?

It doesn't. You mean the Nepomuk-Server, don't you?

Correction: It does, thank you... (I rebooted the computer )
But which are the disadvantages of deactivate the Nepomuk-Server?

You will lose the capability of mail searching. If search is important to you, you may want to check the upcoming 4.13 version of PIM, which is much better in this regard.