The system administrator can define email aliases in the file /etc/aliases. This file contains lines like root:
cwd@mailhost.example.com, /root/mailbox; the effect is the same as having
cwd@mailhost.example.com, /root/mailbox in ~root/.forward. You may need to run a program such as newaliases after changing /etc/aliases.
Note that the workings of .forward and /etc/aliases depend on your MTA. Most MTAs implement the main features provided by the traditional sendmail, but check your MTA's documentation.