Edit the /etc/postfix/main.cf and add/change the myhostname and relayhost details.

 vi /etc/postfix/main.cf

myhostname = vm-130-XXX-XXX-XXX.qld.nectar.org.au
relayhost = [smtp.uq.edu.au]:25

service postfix restart  (or reload)

Test email:

echo "Test mail from postfix" | mail -s "Test Postfix" youremail@griffith.edu.au

##* * * * *
##| | | | |
##| | | | |
##| | | | +---- Day of the Week   (range: 1-7, 1 standing for Monday)
##| | | +------ Month of the Year (range: 1-12)
##| | +-------- Day of the Month  (range: 1-31)
##| +---------- Hour              (range: 0-23)
##+------------ Minute            (range: 0-59)
# /usr/bin/yum -y updated
17 12 2,6,12,17,23,26 1,2,3,4,5,6,7,8,9,10,11,12 * (/usr/bin/yum -y update)  > /dev/null 2>&1