[Exim] Question about MS Outlook 4 Windows

This is slightly off topic but I'll keep it short.

Two years ago I banned the use of MS Outlook where I work (eff.org)
because it was far too vulnerable to viruses. We are using norton
systemworks and I'm filtering executables using one of the EXIM filter
scripts posted here. But at the time Outlook was not only the prime
target of viruses - but had a nasty way of self executing them without
the user having to open up attachments.

But - 2 years have passed and I'm wondering if I should lift the ban on
outlook. I'd appreciate feedback from anyone who is a Sys Admin who has
to deal with this issue.