To authenticate with System.Net.Mail is much more intuitive than it was with System.Web.Mail. No longer do you have to set a fields property. Instead, you simply create a NetworkCredential's object, and set the username and password.

Below is an example setting the username and password.

[ C# ]

static void Authenticate()
{
//create the mail message
MailMessage mail = new MailMessage();

//set the addresses
mail.From = new MailAddress("me@mycompany.com");
mail.To.Add("you@yourcompany.com");

//set the content
mail.Subject = "This is an email";
mail.Body = "this is the body content of the email.";

//send the message
SmtpClient smtp = new SmtpClient("127.0.0.1");

//to authenticate we set the username and password properites on the SmtpClient
smtp.Credentials = new NetworkCredential("username", "secret"); 
smtp.Send(mail);

}

[ VB.NET ]

Sub Authenticate()
'create the mail message
Dim mail As New MailMessage()

'set the addresses
mail.From = New MailAddress("me@mycompany.com")
mail.To.Add("you@yourcompany.com")

'set the content
mail.Subject = "This is an email"
mail.Body = "this is the body content of the email."

'send the message
Dim smtp As New SmtpClient("127.0.0.1")

'to authenticate we set the username and password properites on the SmtpClient
smtp.Credentials = New NetworkCredential("username", "secret")
smtp.Send(mail)
End Sub 'Authenticate