We use Norton for NT, Norton for Exchange, Norton for 9x, etc, across the board. It works 98% of the time, but is only as good as the latest virus signature download. Symantec is sometimes slow on the draw--twice in the last year--reacting to new threats. Not too bad, though.
In February, we had to shut an email server down for an entire day waiting for Symantec to produce the proper virus signature. If MS Exchange or Symantec had built in the simple feature of BLOCKING any email by keywords in the subject or attachment name, we'd be able to block any hostile inbound email.
But, of course, you have to buy another $3000-$6000 third party product to "filter" email by keyword.
Absolute muck!