รยกวน ดู Code ส่ง Email นิดนึงครับ ... An exception of type 'System.Net.Mail.SmtpException' occurred in System.dll

'Imports System.Web.Mail
Imports System.Net.Mail.SmtpClient
Imports System.Net.Mail.MailMessage
Imports System.Data
Imports System.Data.SqlClient
Imports System.IO
Imports System.Data.OleDb
Imports System.Net.Mail
Imports System.Net.Mime
Imports System.Net

Partial Public Class sendemail2
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

    End Sub

    Protected Sub btnSend_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSend.Click

        Dim mail As New MailMessage()
        '*ข้อมูลในส่วน detail
        Dim htmlstring As String = txtDescription.Text
        '*
        '**ข้อมูล EMAIL ผู้ส่ง
        mail.From = New MailAddress("[email protected]", "Support by SMS:Service :: Arkachai CarCare ::")
        '**
        '*** EMAIL คนรับ
        mail.[To].Add(New MailAddress(txtTo.Text))
        '***
        mail.Subject = txtSubject.Text
        mail.IsBodyHtml = True
        mail.Body = htmlstring
        Dim smtp As New SmtpClient("smtp.gmail.com")
        smtp.UseDefaultCredentials = False
        smtp.EnableSsl = True
        smtp.Credentials = New NetworkCredential("[email protected]", "XXXXX")
        smtp.Send(mail)
        mail.Dispose()

    End Sub
End Class