Originally posted here by Panic
I use GroupShield 6 for Exchange from McAfee. Running Exchange 2003 on a single server for about 500 users. I've been using GroupShield since version 4.5 on Exchange 5.5, and have been liking it all the way.
I hate groupshield. Nothing but problems with it. Groupshield 6 is a resource hog on really busy servers. I have 1 8-way HP system running GS6.0 right now and the GS process rpcserv.exe uses up around 40-65% of the total processor. Of course the install for GS5.5 is totally crap and bombs out most of the time when installed on a clustered system. The system usually runs at 45% total processor utilization, but with GS6.0 it runs at 98-100% utilization during peak times. And NAI can't fix it. If you stop GS the processor goes back down to 40% utilization. And we are not the only people having this problem. Do a search on rpcserv.exe and GS6.0 processor utilization and you will get lots of hits on google.

The best answer- go with whomever will give you the software cheapest.

On exchange trendmicro is the best product I have used in terms of setup, ease of use, and functionality. NAI support just sucks.