Postfix Hide Client (MUA) System IP Address / Hostname

I've central mail server gateway. All of our internal systems through this box. How do I remove or hide the hostnames and IP addresses of our internal systems from the messages headers before they go out to other users for security purpose?

Postfix MTA can filter headers using header_check (built-in content inspection) directive. Open main.cf file, enter:
# vi /etc/postfix/main.cf
Now, turn on local recipient checking in the SMTP server, specify the header_checks parameter specifies an optional table with patterns:

header_checks = regexp:/etc/postfix/header_checks

Save and close the file. Create /etc/postfix/header_checks file, enter:
# vi /etc/postfix/header_checks
Ignore 127.0.0.1, 10.24.55.1 and 192.168.0.[0-9] IP address (regex) from the headers :

/^Received:.*\[127\.0\.0\.1/      IGNORE
/^Received:.*\[10\.24\.55\.1/ IGNORE
/^Received:.*\[192\.168\.0\.[0-9]/      IGNORE

# postmap /etc/postfix/header_check
# service postfix reload
OR
# service postfix restart
See header_check(5) man page for further details.