My purpose is to setup two MX servers in different locations for high availability.
I'm not sure I understand your question, but I guess that what you want is a secondary MX in case the primary MX becomes unavailable for some reason (power outage, server crash, whatever). If this is indeed what you want to do, you could check http://www.postfix.org/STANDARD_CONFIGURATION_README.html#backup , or https://www.howtoforge.com/postfix_backup_mx , or any other howto.
Gregory
