You can change the recipient to whom the root mails from server are delivered as follows.

1) Go to /etc/aliases

2) Scroll down to the bottom where you will find a line as follows.

# Person who should get root’s mail
root: mark

If you want to send this to some other email address, say mark@gmail.com, make the line looks as follows.

# Person who should get root’s mail
root:  mark@gmail.com

Once the change is done, save and close the file. In order for the changes to be picked up by postfix, you need to issue the following command.

# newaliases

Once that is done, try sending a mail to the root ID and see how it goes !!