Did you set SMTP correctly
Make sure Kmail SMTP is set right. I had an issue where it was attempting to use send mail instead of connecting to my outgoing SMTP server. Also in Indentities make sure that you have it set to the email address you want Kmail to identify you under. It defaults to using your hostname settings and that can cause this issue as well.
--Shaun
It isn't about it being free, rather its about the freedom it brings.