Event extensions enable developers to add to or override behavior such as the arrival of new messages, reading and writing messages, sending messages, reading and writing attached files and tracking selection changes in a window. For example:
You can write an extension that transparently scans message attachments for viruses. When a message is received in a user's Inbox, the "message received" event would trigger the virus detection program and the user could be prompted to take action if a virus was found. This is especially useful in environments where users routinely attach executable programs to messages.
You can write an extension that compresses and decompresses messages when certain messaging events are detected. This can be especially useful in an environment where large messages, such as attached documents containing bitmaps, are routinely sent.