Every so often you find a simple yet powerful application that just rocks. OWANotify is one of those utils and even better - it is freeware! (Though if you like it you can make a contribution to the author)
This utility - like many other mail notification utilities I have seen puts an icon in the system tray and checks you inbox at a specified interval. If a new message arrives then a popup notification is displayed. Unlike most others - which check the inbox over POP or IMAP - OWANotify checks for new email by logging into Outlook Web Access over HTTP or HTTPS. Let me add here that if you have OWA exposed to the internet you should be using HTTPS.

The user can then click the icon to open the mailbox, or right-click the icon for other options as shown below.

This great little tool has helped me overcome an issue I have been struggling with for a while - effectively monitoring TWO mailboxes on for different organisations. Using OWANotify I can log into my work email at work using Outlook and point OWANotify at my inbox on my Exchange server at home. Conversly when I am at home I can still keep an eye on my work email if need be. Yes I am that much of a geek.
The tool will also be of use to users who only use OWA and don't have the full Outlook client installed. While OWA can display popup notifications when new messages arrive it only does this if you have a OWA window open. If the user closes the window or navigates away from it the notifcations stop.
A truley excellent application and a must have if you use OWA frequently. For more information and the download visit the OWANotify site.