If the root user is getting mail on your server (for example from cron scripts) then it can really helpful to forward it to an external email address. There are two ways of doing this:
1) The easiest and quickest way is to make a file in the folder called /root/.forward and place your email address in it. Note – this will work for any user.
2) Alternatively you can edit the /etc/aliases and add the following line:
Then restart postfix (assuming this is you mta).
service postfix restart
Either way you can then test your configuration but sending an email:
echo test | mail -s "test message" root
p.s. You can install the mail command for this test using apt-get install mailutils 🙂