We use Lotus Notes. Superior email. Superior groupware. No viruses piggybacking the mail - we catch it and innoculate it at the firewall.
The only way viruses get in is via the users who deem themselves too good to follow standards and install the horrible Outlook on their laptops. I've missed many a meal over the years to run to the aid of these "revenue producers". Seriously, how can you send these people out in public when they can't even be trusted to follow simple instructions? Its like not knowing how to loosen the vice that one's testicles are clamped in. And you enable it.
I have only seen Outlook a few times, but it seems that preview box opens attachments without you asking. Just scanning through the inbox is all it takes to open a nasty. Is that correct?
I normally use exchange and you have to double click on attachments to open them. BTW. I bet I have gotten 50 of those 'gone' e-mails today. My name is near the top of a large, multi-national address box and as the day has gone on this virus is literally spreading all over the world judging by the addresses of the senders.
We use Groupwise and have the same advantages. We block attachments such as .pif, .scr and .vbs because there is no legitmate reason to allow them in.