Dim SmtpServer As New SmtpClient()
        SmtpServer.Credentials = New Net.NetworkCredential("xxx@gmail.com", "password")
        'SmtpServer.Credentials = New Net.w
        SmtpServer.Port = 587
        SmtpServer.Host = "smtp.gmail.com"
        SmtpServer.EnableSsl = True

        mail = New MailMessage()
        Dim addr() As String = TextBox1.Text.Split(",")
        Try
            mail.From = New MailAddress("xxx@gmail.com", "Web Developers", System.Text.Encoding.UTF8)

            Dim i As Byte
            For i = 0 To addr.Length - 1
                mail.To.Add(addr(i))
            Next
            mail.Subject = TextBox3.Text
            mail.Body = TextBox4.Text
            If ListBox1.Items.Count <> 0 Then
                For i = 0 To ListBox1.Items.Count - 1
                    mail.Attachments.Add(New Attachment(ListBox1.Items.Item(i)))
                Next
            End If
            mail.DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure
            mail.ReplyTo = New MailAddress(TextBox1.Text)
            SmtpServer.Send(mail)
        Catch ex As Exception
            MsgBox(ex.ToString())
        End Try