I have been struggling with that one too. There is a lot of information on the Internet
about that one. After searching for a quite a while I found that I had to set the SmtpServer
to the empty string, like this...
SmtpMail.SmtpServer = "";
Naturally it doesn't work on my local environment, but when deploy the project at my web hotel it works. I am not saying that this will solve your problem, since the error can be a lot of things. However, I would like to have saved the time trying this to start with.
Let me know if it works,