Please give us your best suggestion how to place this server. Or is there something you could recommend that I should do in current setup to prevent this security issue?
You can make your e-mail server sit behind you proxy and make your e-mail server "server proxied" to the proxy server. Install a good enterprise version anti virus software and have it integrate with your mail server to scan all incoming and outgoing messages. Also, stop SMTP relay on your mail server. And if you decide to switch to MS ISA, you won't need separate Web Filtering software -- it comes built in.
This was first published in October 2003