Astaro v8 in esx 3.5

Hi All

New to Astaro - so forgive stupid questions.

I have been trying to get astaro to work as a spam filter without luck.

Setup is:

ESX 3.5 (no vCentre)
3 x 1Gb NIC (1 on board plus 2 x expansion) -all Intel based detected by ESX

Current VM is an Exchange 2003 box.

New Astaro VM build from the hardware ISO as I can't import OVF files on this version of ESX without vCentre.

I am confused how I should have the network cards set up. Should I have 1 x NIC for service console (which it currently is) and the other two for the Astaro box? I have a modem/router with inbuilt firewall that takes care of firewall so dont need Astaro to act as my authentication point with my ISP.

The way I have it configured is:

Router --> vSwitch0 ((Onboard NIC) Service Console + Astaro External) vSwitch 1 (Astaro Internal NIC (using other another NIC)) out to Netgear Network switch into remaining NIC which the Exchange server lives on.

I know I am missing something basic here - do i need a 4th NIC?

Also, when I apply the base license it mentions that SMTP scanning is not available - is this something new in v8?

As mentioned, all I want to do is use it as a SPAM filter to block spam which in turn should block virus laden email.

Any help is very much appreciated