Send from not managed domain

[badaim]

Hello,

I have ZCS Network Edition which manage multiple domains.
Now i have few workes, who need to recive and send emails from domain, that is not managed by zimbra. Its managed by external server (mailing lists,forwards mail), and there is no option to create account on it. So i did these steps:
1. I create domain (an example abc.net)
2. Then I could add an alias from domain abc.net to account in domain that is managed by Zimbra ( example user@abc.net -> user@abc.zimbradomain.net)
3. Then i added in account options, ability to send from domain abc.net)

And everything works great, except situation, when user want to send email to user in domain abc.net, which don`t have account in my Zimbra. Only external server knows where forward it, but Zimbra is looking in local users table (she "thinks" that she manage that domain).

How can I resolve this problem ?