I am trying to lock down postfix so the zimbra server doesn't behave as an open relay.

I tried modifying main.cf with the;

smtpd_sender_restrictions = check_sender_access hash:/opt/zimbra/nice_guys

and adding to;

smtpd_client_restrictions = reject_unauth_pipelining, check_client_access hash:/opt/zimbra/nice_guys

But as soon as I save and issue a postfix reload, the main.cf appears to get overwritten.

What have I missed pls?