Can I change root's email address or forward it to an external address?

Any user, including root, can forward their local email by putting the forwarding address in a file called ~/.forward. You can have multiple addresses there, all on one line and separated by comma. If you want both local delivery and forwarding, put root@localhost as one of the addresses.

The system administrator can define email aliases in the file /etc/aliases. This file contains lines like root: [email protected], /root/mailbox; the effect is the same as having [email protected], /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.

Simply create /root/.forward and place your email address in this file. It will be forwarded to your external mail address.