was the only host that could deliver the mail. These conditions still exist in some locations, but a more common reason that this configuration is popular is because network managers want to route all outbound mail through a single server for increased security, simplified queue management, and centralized logging. See Also Section 4.3.3.6 in the sendmail book discusses the SMART_HOST define. 3.3 Passing Local Mail to a Mail Hub Problem You have been asked to create a sendmail configuration that sends all local mail to a mail hub, while directly delivering mail addressed to external systems. Solution Create a sendmail configuration containing the MAIL_HUB define to identify the mail relay host for local mail. Use the LOCAL_USER command to exempt the root user's mail from relaying. Here are sample commands: dnl Define a relay server for local mail