What version of nopCommerce? Does the "test" email work? You probably should speak to your ISP support to be sure you have the correct settings. When you say "ISP" do you really mean 'internet service provider', or do you mean the Hosting company? (or are they one and the same?)
The application does not use an SMTP "Server"; it uses a SMTP Client to talk to the server. Does the "test" email work? What are your settings? (post them here except dummy your domain and password)