per user email restrictions

I'd like to apply certain rules to certain users on my system...to
illustrate, lets say I have two user "groups", A and B.

In group A, I want them to only to be able to send/receive email from group
A and B, AND NOT to/from the internet. However, in some special cases, I
want a particular user in group A (or everyone in group A if I can't do per
user) to be able to email someone on the internet and then allow the
internet user to respond to that particular member from group A.

In group B, they have unrestricted access, just like normal. They can email
whoever they want to.

I've tried
http://www.stahl.bau.tu-bs.de/~hilde...ion_classes2.s
html
and that works for denying users that are sending to group A, but it does
not solve the problem of group A sending to the internet.

I am aware of a per-user UCE patch at
http://www.kfki.hu/~kadlec/sw/postfix_patch.html but that is for a very old
version of postfix.

Can someone help me with this? I've been working on it for almost three
days and I am out of ideas.

-joe