Tray Helper it's freeware, award winning application with many features (f/e: email checker, auto mail responder, anti-spam, popup-killer, event reminder and more).
There was a new version (4.3) released recently (July 21, 2004) with following changes:

- New e-mail address book. It's now fully integrated with Windows address book.
- Added feature to bounce e-mail messages - send back error like message to the sender, so this person will think that your e-mail account is no longer valid.
- Many small improvements in e-mail composer module (for example added "reply all" button).
- Improved e-mail filters ("white list" of addresses is now more intelligent).
- Some improvements in THOnline service (tracking e-mail messages).
- Removed few bugs and added some less important features.
- Minor improvement in user interface of application.