Sending emails with KMail stopped working

Dear List, I am not able to send mails with KMail anymore (I am writing this with mozilla). Receiving works ok. I get an error from the mail server that: "No valid recipients specified" I am sure that the addresses are correct. I used reply to addressees I had used before. I am using SuSE 8.1 and KDE 3.1.3. I am the one who killed his KDE a few mails ago, It's working again- I had to disable socks in KDE - , but I don't think the mail-send problem now has to do with this, as KMail is actually talking to the server. How can I see what KMail actually sends to the server? Kostas