purvis
You can use server & gateway mode with the static IP option thus creating a DMZ for an additional layer of security.
With system policies in place on Windows workstations you can stop users "doing things they should not" and also prevent them from changing workstation setup etc, you can "lock down" your workstations very tightly indeed.
But you are very wrong about not hitting emails with all you got in a server.
I am not sure what you actually mean.
I do hit emails with "everything the server can do" and I receive very little spam & only the occasional virus infected email. Usually any virus infected email is sitting in the junkmail folder as spam techniques have already detected that message as being problematic.
That's a good example of the point I am making re anti virus "techniques", as detecting and/or filtering and/or blocking those spam source or spam content messages, does also detect virus laden messages due to common elements within them.
I referred to a secondary (ie additional) layer of virus protection being in the workstations, which should not be alterable by users. That is there to catch anything that occasionally slips through the primary layer of protection in the server, ie scanners & filters etc. It also protects the workstation from viruses coming from sources other than email messages. Real time & heuristic detection catches as yet unknown viruses.
The point I am making which you seem te be overlooking, is that multiple additional virus scanners (on your server) are not likely to prevent virus infected email messages "getting through" on "day 1" of a new virus being released. If all four scanners do not yet know about the virus then they will not detect it, so having four scanners gives no immediate benefit compared to one scanner.
Other server level techniques (such as those previously mentioned ie executable content in attachments is a good one. block spam/virus sources is also a good one etc) which do not use or rely on virus definitions, are more likely to catch email messages with "unknown viruses" on "day 1".
Anyway you are free to do whatever you want & spend your time as you please, It's just to me that you seem to be investing time & research into areas that will not necessarily be that beneficial, & are covered by existing available techniques should you choose to use them.