SMTP -- Configure an MTA to forward (relay) email through a smart host

This is actually quite simple. You need to modify the following line in the postfix config file (/etc/postfix/main.cf):

relayhost = 10.168.20.227

This will relay emails to host 10.168.20.227, which means that this host needs to be configured as Postfix server, see my previous post here.

Note that you still need to change other configuration settings as detailed in my previous post.