SASL is the way to go. If you use smtpd_sasl_auth_enable (along with smtpd_relay_restrictions = permit_sasl_authenticated and a proper SASL configuration), only authenticated connections will be able to use your server as a smarthost relay.
Article ID: 113, Created: 4/23/2025 at 3:52 PM, Modified: 4/23/2025 at 3:52 PM