When you post your configuration for assistance with postfix it's best to post the output of the command postconf -n
that will show us ONLY changes you have made frodefault settings making it easier to spot what might be wrong.. Also if you folloewed a specific how-to to configure teh system referencing a link to that can be helpful as well.. just fyi for the future.
You want to read this.. http://www.postfix.org/SMTPD_ACCESS_README.html
Your current restrictions.. not much..
Some suggested restrictions..
For 2.x versions of Postfix:
smtpd_helo_required = yes
disable_vrfy_command = yes
you will need to read up on the additional restrictions, especially the ones I turned gray..
the gray entries refere to additional configuration files you need to create if you decide to use those options. .