Restrict Certain Users

One of our Zimbra servers is running an old version Release 6.0.12_GA_2883.RHEL5_20110306010832 CentOS5 FOSS edition - we hope to plan on upgrading soon.

I was reading through the forums and looking for a way to restrict specific groups of users to only be able to send to a specific domain.

I did come across;
http://forums.zextras.com/zimbra-howto/164-how-restrict-outgoing-email-well-external-web-access-certain-users.html
Wanted to know if this would work with our version, also if this could be done by groups membership instead of individual users one at a time?

Thanks in advance.

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