Forwarding mail for the root user to an external address

Quite often I find mail such as those generated by cron jobs are sent to the user they are executed under - for example root.

Using the 'aliases' file we can instruct any mail destined for a specific user to be forwarded to another (internal or external) address - for example by adding the following to /etc/aliases:

sudo vi /etc/aliases

root: yourname@externalemail.com

and ensure those changes take effect by issuing:

sudo newaliases

and finally reloading the mail server:

sudo service postfix reload