Go to Settings and click Configure KMail...
Click Identity and add your name (anything you like) and email address (must be the full email address and spelled correctly).
Click Accounts or Network. Under the Receiving tab, press the ADD button and add your incoming email information. The Accoutn Name or Login must be the fuyll email address. The Host should be "mail.yourdomain.com". Click OK to close.
While still on Accounts or Network, switch to the Sending tab. Press the ADD button and add your outgoing email information. Use SMTP and Host is again "mail.yourdomain.com". Be sure to check the "Server requires authentication" box if you have one. Click OK to close.
Click OK again and you should be able to use your email.