[c#] How to set username and password for SmtpClient object in .NET?

Since not all of my clients use authenticated SMTP accounts, I resorted to using the SMTP account only if app key values are supplied in web.config file.

Here is the VB code:

sSMTPUser = ConfigurationManager.AppSettings("SMTPUser")
sSMTPPassword = ConfigurationManager.AppSettings("SMTPPassword")

If sSMTPUser.Trim.Length > 0 AndAlso sSMTPPassword.Trim.Length > 0 Then
    NetClient.Credentials = New System.Net.NetworkCredential(sSMTPUser, sSMTPPassword)

    sUsingCredentialMesg = "(Using Authenticated Account) " 'used for logging purposes
End If

NetClient.Send(Message)