This feature is new in the Solaris Express 1/04 release.
The contents of the /usr/lib/mail directory, which might be in a read-only file system, are now in the /etc/mail/cf directory, which is writable. This change better supports m4 configuration. Note, however, these exceptions. The shell scripts /usr/lib/mail/sh/check-hostname and /usr/lib/mail/sh/check-permissions are now in the /usr/sbin directory. For backward compatibility, symbolic links point to each file's new location.
For further information, see the System Administration Guide: Network Services.