I got it working. SMTP Host is relay-hosting.secureserver.net, port is 25, and as stated above "From" address must be an email address with the same domain, and if you want to reply to the sender use advanced settings and pass the sender's address dynamically. The form is sent within seconds. GoDaddy's help was useless, I found the solution in a forum elsewhere.
On another issue though, in WebAssist, the help system says the email form template will open for editing in WebAssist. It did not and I had to edit the form manually. Can you help with that?