===== Postfix client configuration =====

http://www.certdepot.net/rhel7-configure-central-mail-server/

Add the following lines in your postfix main config file (for info only relayhost is required, most time):
<cli prompt='#'>
[root@centos7 postfix]# cat /etc/postfix/main.cf
...
mydomain = mydomain.org
...
myorigin = ganglia.mydomain.org
...
inet_interfaces = all
...
inet_protocols = ipv4
...
mydestination = $mydomain
...
relayhost = [smtp.mydomain.org]:25
...
</cli>

Reload postfix config
<cli prompt='#'>
[root@centos7 postfix]# postfix reload
</cli>

Test to send an email
<cli prompt='#'>
[root@centos7 postfix]# sendmail -v myemail@mydomain.lu < /etc/motd
Mail Delivery Status Report will be mailed to <root>.
</cli>

Add an alias to redirect root mailbox to serveradmin@mydomain.lu, and reload alias DB using sendmail -bi or newaliases
<cli prompt='#'>
[root@centos7 postfix]# vi /etc/aliases
...
root:           serveradmin@mydomain.lu
[root@centos7 postfix]# sendmail -bi
</cli>

Check errors in /var/log/maillog
<cli prompt='#'>
[root@centos7 postfix]# cat /var/log/maillog
</cli>