The message will stay in the 'outbox' folder

From time to time Kmail on my Suse 9.3, KDE 3.5 frustrates me with the following information: Sending failed: Connection to host smtp.indo.net.id is broken. The message will stay in the 'outbox' folder until you either fix the problem (e.g. a broken address) or remove the message from the 'outbox' folder. The following transport protocol was used: Bonet direct What I really like to know what to do the next time this message pops up. And what is the cause: connection broken or a broken address which is quiet different. I expect a clearer answer from Linux. This not Windows.