Introduced in the Solaris Express 8/04 release, sendmail version 8.13 is the default in the Solaris 10 OS. Although this new version of sendmail provides many new features, the FallBackSmartHost option is the most significant addition.
Because of the FallBackSmartHost option you no longer need to use main.cf and subsidiary.cf. The main.cf file was used in environments that supported MX records. The subsidiary.cf file was used in environments without a fully operative DNS. In such environments a smart host was used instead of MX records.
The FallBackSmartHost option provides unified configuration. This option operates like an MX record of last possible preference for all environments. To ensure that mail gets delivered to clients, this option, if enabled, provides a well-connected, or “smart,” host that serves as a backup or failover for MX records that fail.
sendmail Version 8.13 also provides the following:
Additional command-line options
Additional and revised configuration file options
Additional and revised FEATURE declarations
For more information, see the System Administration Guide: Network Services.