STARTTLS cannot be enforced. It will be used automatically if the mail server supports it. The encryption type should be grup to ‘None/STARTTLS’ in this case. See here for an example on how to configure self signed certificates. If you permit downloading of documents by the third party, you birey https://www.saludcapital.gov.co/sitios/VigilanciaSaludPublica/Lists/Contactenos/DispForm.aspx?ID=2972663