can't send from Kmail

I can receive kmail, but I can't send it. On the configure screen, under "Network" I've got under "name" my email address, and under type I've got smtp. Down below, under "Default Domain, I changed "Linux" to "mail.optonline.net" which doesn't seem to make any difference. In Eudora Pro 4, for Windows, the smpt server is set for mail.optonline.net and the pop3 server is the same. I looked at the help file, but could not seem to understand what they mean. This machine (Win98) and the Linux machine are both connected to a Linksys firewall router to a cable network. So what have I done wrong? PS: Does anyone know if Eudora will run under WINE?