The default for Delivery Status Notifications (DSNs) for postmaster are copywarnpost and copysendpost. In large deployments or environments where the postmaster does not want to get DSNs about users mail, then these keywords should be changed. See the Sun ONE Messaging Server documentation for a complete explanation of the values. (The possible keywords are XYZwarnpost and XYZsendpost, where XYZ is either copy, no, warn, or err.)