An alias allows to redirect mail sent to a given address.
Mail alias database is usually kept in flat-text format in the file /etc/aliases
# /etc/aliases mailer-daemon: postmaster postmaster: root
This aliases postmaster to root, so that any mail sent to postmaster will instead be delivered to root.
So to redirect root mail to a real email account just add this line:
# /etc/aliases mailer-daemon: postmaster postmaster: root root: email@example.com
or if you do not want to see any of that mail change it to:
root : /dev/null
Every time you make changes to /etc/aliases, you must run newaliases to update the database.