6. The method of claim 5 , wherein prior to said identifying, by an anti-virus detection module running on the network gateway computer system, a type and associated structure of the archive file, determining, by the transparent proxy, whether there exist one or more attachments associated with the email message and if so, then causing the one or more attachments to be scanned by the anti-virus detection module.
5. The method of claim 1 , wherein said receiving, at a network gateway computer system logically interposed between a client workstation and an email server, an archive file that is in transit across a network as an attachment to an email message destined for the client workstation comprises intercepting the email message by a transparent proxy running on the network gateway computer, the transparent proxy implementing simple mail transfer protocol (SMTP) handlers for a subset of SMTP commands and replies.