You need to change from localhost to the host name of your mail server, you need to put a valid username and password for your mail server and the correct port for your mail server.
I would first test it using the appSettings settings and use the Contact form feature to send yourself an email. Once you get it working there then make the same settings in system.net mailsettings section. Put a contact form on a page, click the gears to edit settings for the contact form and put your email address there.
If you can't get the settings correct in the contact form then you need to check with the administrator of your mail server for correct settings.
If the settings are correct it will work. If the settings are not correct there is nothing I can do to help.