I see in this Restrict users to certain domain - Zimbra :: Wiki

I follow that wiki,it's work.
But I want to setup like this
Default user is allow to send local (restrict domain) only.
Default user means. When you add a new user to zimbra. It can send only locally.
For user who is allowed to send email to outside, need to config in some where.

that wiki config some user cannot sent to outside ,If I do that when admin create new user he need to update that user in restricted_senders file.

It's not comfortable.

How I do

Thank you for reply.