ASP.net联系表发送电子邮件错误

Question

i really need help on one thing. I have a website and in that website i have contact us page in which the users can contact the admin about the page or any other stuff.

The problem is when i try to render the page, it gives me an error saying

The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. Learn more at
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Net.Mail.SmtpException: The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. Learn more at

Source Error:


Line 21:         smtp.Credentials = NetworkCred
Line 22:         smtp.Port = 587
Line 23:         smtp.Send(mm)
Line 24:         lblMessage.Text = "Email Sent SucessFully."
Line 25:     End Sub


Source File: C:\Users\user\Desktop\ContactUsForm\VB.aspx.vb    Line: 23 

I really don't know wt to do. My VB behind code is :

Imports System.Net
Imports System.Net.Mail
Partial Class VB
    Inherits System.Web.UI.Page
    Protected Sub btnSend_Click(ByVal sender As Object, ByVal e As EventArgs)
        Dim mm As New MailMessage("sender@gmail.com", "reveiver@gmail.com")
        mm.Subject = txtSubject.Text
        mm.Body = "Name: " & txtName.Text & "<br /><br />Email: " & txtEmail.Text & "<br />" & txtBody.Text
        If FileUpload1.HasFile Then
            Dim FileName As String = System.IO.Path.GetFileName(FileUpload1.PostedFile.FileName)
            mm.Attachments.Add(New Attachment(FileUpload1.PostedFile.InputStream, FileName))
        End If
        mm.IsBodyHtml = True
        Dim smtp As New SmtpClient()
        smtp.Host = "smtp.gmail.com"
        smtp.EnableSsl = True
        Dim NetworkCred As New System.Net.NetworkCredential()
        NetworkCred.UserName = "sender@gmail.com"
        NetworkCred.Password = "senderpassword"
        smtp.UseDefaultCredentials = True
        smtp.Credentials = NetworkCred
        smtp.Port = 587
        smtp.Send(mm)
        lblMessage.Text = "Email Sent SucessFully."
    End Sub
End Class

The error is at line 23 where it is saying smtp.Send(mm)

I am really in a need. Please can anyone help me.

Answer 1

Change

smtp.UseDefaultCredentials = False

your don't want to use the default credentials, you want to use the credentials you created in your code.

https://msdn.microsoft.com/en-us/library/system.net.mail.smtpclient.usedefaultcredentials(v=vs.110).aspx