Impossible postfix

Hi, HAving spent many a ltae evenings I am beginning to give up on postfix. I have a small network at home and want to send mail from the network to the outside world. I have a permanent internet connections. I have specified in the main.cf file correct domain name, correct network parameters etc..., and I can query postfix on the server and get it to send emails...what I can't do is send a mail with Kmail .. the mail log shows as far as I can see that postfix sees Kmails attenpt to email but refuses the connection. Does anyone have any idea why postfix refuses the connection...is there something that should be changed in the master.cf file? Thomas