Cannot send emails with ASP.NET

Hi all,

Im receiving the following message when I try to send an email (ASP.NET)

The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.3 Client was not authenticated

I configured SMTP already (IIS6) and selected INTEGRATED WINDOWS AUTHENTICATION.

But still not working.

Here's the code Im using:

Any ideas?
If System.Text.RegularExpressions.Regex.IsMatch(F1.Text, "^[a-zA-Z][\w\.-]*[a-zA-Z0-9]@[a-zA-Z0-9][\w\.-]*[a-zA-Z0-9]\.[a-zA-Z][a-zA-Z\.]*[a-zA-Z]$") = True Then
                Dim msg As New System.Net.Mail.MailMessage
                Dim smtp As New System.Net.Mail.SmtpClient
                Dim addrFrom As New System.Net.Mail.MailAddress("", "Welcome to My Domain")
                msg.IsBodyHtml = True
                msg.From = addrFrom
                msg.Subject = "Test"
                msg.Body = "Test"
                smtp.Host = ""
                smtp.Port = 25
                smtp.DeliveryMethod = Net.Mail.SmtpDeliveryMethod.Network
                smtp.Credentials = New System.Net.NetworkCredential("Administrator", "xxxxxxxxxxx")
            End If

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Maybe use domain\username rather than just administrator?
If this is not on a domain, then use machinename\username and see if that works?

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The better way is to use smtp setting from web.config, than hardcoded one.
And if ASP.NET application is working on this same machine as SMTP, than you can use PICKUP delivery method instead of NETWORK (site will put EML file in your pickup directory, and SMTP will handle this).
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