What do you do when you get a request to forward root and system emails to a human user? Why you remove root user from the system mail recipient and add in human user email address. I wouldn't recommend this, because everything will get emailed to you instead of going into root user's mailbox on the host
Anyways, if you want to go ahead and do it, then this is how you do it. Please make a backup copy of /etc/aliases before you clobber it. I've tested this on Linux distros
# vi /etc/aliases
# It is probably best to not work as user root and redirect all
# email to "root" to the address of a HUMAN who deals with this
# system's problems. Then you don't have to check for important
# email too often on the root account.
# The "\root" will make sure that email is also delivered to the
# root-account, but also forwared to the user "joe".
#root: joe, \root
Note : You have to run the command newaliases each and every time you modify the /etc/aliases file for new changes to take effect