If I've already got Postini what value add would installing GroupShield for Exchange provide???

More specifically internal emails within the co. (10K employees) are not scanned but all nodes on the network should have McAfee VSE On-Access Scanning enabled and current (about 95% compliant). So if a threat attempted to propogate wouldn't OAS on the individual machines catch it? Why have emails scanned on exchange? It seems duplicitous...

Any thoughts would be welcome!
Thanks,
cupa

For 10k employees I would advise Forefront TMG.

That's interesting because Forefront just came up in conversation. We have an EA agreement with Microsoft and we're due to renew this June...whenever this happens there's opportunity for negotiation and MS is always of course trying to get us to adopt any # of additional products. What's the advantage of Forefornt over GroupShield? And I wonder if anyone has a response still to my original inquiry... Do I really need a mail server email scanning software if I already have an affective on-access scanning strategy???
Thanks!