http://technet.microsoft.com/en-us/library/aa997907(v=exchg.80).aspx
http://technet.microsoft.com/en-us/library/aa996905(v=exchg.80).aspx
Download Setspn.exe from ms:
http://www.microsoft.com/download/en/confirmation.aspx?id=25233
Check the entries you have:
setspn.exe -a SMTPSVC/mail.computerladen.ch mail
setspn.exe -a HOST/mail.computerladen.ch mail