How do I send mails without password using VB.NET

the smtp server requires a secure connection or the client was not authenticated 5.7 57

Try
            ServicePointManager.ServerCertificateValidationCallback = _
        New System.Net.Security.RemoteCertificateValidationCallback(AddressOf customCertValidation)

            Dim Smtp_Server As New SmtpClient
            Dim mailobj As New MailMessage()
            Smtp_Server.UseDefaultCredentials = False
            If rbtnWithPass.Checked = True Then
                Smtp_Server.Credentials = New Net.NetworkCredential(txtFrom.Text.Trim, txtPassword.Text.Trim)
                mailobj.Subject = "Test mail with password"
            Else
                Smtp_Server.Credentials = System.Net.CredentialCache.DefaultCredentials
                mailobj.Subject = "Test mail without password"
            End If


            Smtp_Server.Port = txtPort.Text.Trim
            Smtp_Server.EnableSsl = False
            If rbtnServer.Checked = True Then
                Smtp_Server.Host = txtServerName.Text.Trim
            Else
                Smtp_Server.Host = txtServerIP.Text.Trim
            End If

            mailobj = New MailMessage()
            mailobj.From = New MailAddress(txtFrom.Text.Trim)
            Dim toArr As String()
            toArr = txtTo.Text.Trim.Split(",")
            For Each toStr As String In toArr
                Dim val As String = toStr.Replace(vbLf, "")
                mailobj.[To].Add(val)
            Next
            Dim ccArr As String()
            ccArr = txtTo.Text.Trim.Split(",")
            For Each ccStr As String In ccArr
                Dim val As String = ccStr.Replace(vbLf, "")
                mailobj.CC.Add(New Net.Mail.MailAddress(val))
            Next
            mailobj.Body = txtBody.Text.Trim + vbLf + vbLf            

            Smtp_Server.Send(mailobj)

            MsgBox("Email send successfully. From:" & txtFrom.Text.Trim & " To: " & txtTo.Text.Trim & " Time : " & Now)
        Catch ex As Exception
            MsgBox(ex.ToString)
        End Try

Private Function customCertValidation(ByVal sender As Object, _
                                              ByVal cert As X509Certificate, _
                                              ByVal chain As X509Chain, _
                                              ByVal errors As Net.Security.SslPolicyErrors) As Boolean

        Return True