For more information, see Using Your Assigned Administrative Rights in Securing Users and Processes in Oracle Solaris 11.4.
An entry for each mail client
# cat /etc/mail/aliases .. alias:expanded-alias
Use the short alias name
Use the expanded alias name (user@host.example.com)
A Postmaster: root entry
# cat /etc/mail/aliases .. Postmaster: root
An alias for root using the mail address of the person who is designated as the postmaster
# cat /etc/mail/aliases .. root: user@host.example.com
Use the assigned address of the designated postmaster
# cd /var/yp # make
The changes in the /etc/hosts and /etc/mail/aliases files are propagated to NIS slave systems.