I've searched the forums, but have not found a conclusive answer to this issue. I have a user that is attempting to send a message to an outside domain through the Zimbra client. When hitting send she gets:

Critical: Message not sent; one or more addresses were not accepted.
Rejected addresses: mary@domain.org
I ran an nslookup/dig against the domain and they have a valid mx record:

Server: 10.10.56.20
Address: 10.10.56.20#53

Non-authoritative answer:
domain.org mail exchanger = 10 SMTPGATEWAY.domain.org.

Authoritative answers can be found from:
domain.org nameserver = NS15.WORLDNIC.COM.
domain.org nameserver = NS16.WORLDNIC.COM.
SMTPGATEWAY.domain.org internet address = xxx.xxx.xxx.xxx
But 'zmprov gd' returns:
ERROR: account.NO_SUCH_DOMAIN (no such domain: domain.org)
I have DNS lookups enabled in the admin UI.