Exchange calls it connectors...

[Omnicef]

Hi everyone. Thanks for the help (in advance). I have Zimbra running on a machine with about ten users. They love their new server except for one thing. They cannot send to att.net or sbcglobal.net. I know the problem is actually an att problem (they keep getting added to their internal dnsbl) for absolutely no reason. I have seen this before. In exchange I would create a connector for just those domains and relay them through my office email server. How do I do that in Zimbra? I do not want to be a smarthost for all their email, just att owned domains. Any ideas? I can't figure it out.