To close this thread I'll post the ultimate resolution. As the WebAssist doc states, the settings for host and port can usually be left blank. That is what eventually worked for me on Yahoo hosting. However, when I was initially using those simple settings, I had the email From field set to a random user, not from an email address within my domain. Yahoo doesn't allow an email to originate from other than your domain. So it failed. I assumed the host and/or port was wrong and attempted numerous other values, including those specified in writting on Yahoo's site. The real issue the entire time was my "From" email address. When a Web Assist professional helped me and we went back to blank host/port and an email From address within my domain, all worked.