Hey,

Not much to say here because everything is already explained in the GitHub README file.

In a few words, I wrote a script that extracts from Active Directory LDAP all Exchange email addresses and export this as a Postfix map. The idea is to be able to reject invalid recipients instead of whitelisting the whole domain. By doing this, your infrastructure will stop sending “non-delivery notifications” back to forged sender addresses because you let some invalid recipient emails go into your system.

Everything is available there:
https://github.com/eLvErDe/exchange-active-directory-to-postfix-map