Assuming it is a Unix system:
configure the new machine to have the same IP, hostname, and everything else iqual to the first one.
Stop all services (messaging, Directory and Admin) and tar your NetscapeRootDir (by default /usr/netscape/server4)
Ftp to the new machine, ftp the one or 2 files messaging puts in /etc (it should be simple to find) and, change your /usr/lib/sendmail to the correct symbolic link.
start everything.