I created the following code to implement this in the Outlook plugin and attached it to a menu item for testing. It was, in fact, successful in removing the new mail envelope from the taskbar. Now, the *really* tricky part is figuring out when to remove the icon.

I don't know how they do it, but Cloudmark SpamNet (which is a voting-system filter -- email is treated as spam if other people who use SpamNet report it as spam) does a pretty good job of doing the right thing. Only maybe 1 in 200 times is it wrong. I would guess that whenever it starts to process a new email (or perhaps periodically), it first reads the current state of the icon (no idea how to do that), then processes the mail, and then clears it if necessary. For example, when a spam arrives in my inbox, I do see the icon come on, and then when SpamNet moves the spam out a few seconds later, it turns it off. Furthermore, when it's a non-spam, the icon remains on. I've never seen a case where it is OFF when it should be ON, but I have seen a bunch of cases (maybe 1 or 2 a week) where it is ON when it should be OFF. By the way, I've been using SpamBayes and SpamNet together for the last week, and have no false positives, no false negatives, and only a few unsures to deal with. For me, both product filter about 90% of the spam, but luckily, the missing 10% in each do not seem to overlap. The very tiny spam emails that contain only a URL SpamNet seems to miss, but SpamBayes gets them. The long spams frequently turn up as Unsure by SpamBayes, but SpamNet gets them fine. I do this by having SpamNet make the first pass, and then SpamBayes is set for a 10 second delay in background processing, so it gets to look at anything that SpamNet missed.