I'm using a locally installed version of the Zimbra OSS and I'm very interested in the possibility of invoking a WebService on certain events. An illustrative scenario would be this:

A user creates a new meeting for next friday with some attendees and, for each attendee, instead of sending an email, the server invokes a WebService.
Then, next friday, five minutes before the meeting is meant to start, the system invokes another WebService as a reminder, instead of the classic pop-up reminders that are only shown to users (attendees or creator) that are logged on the server web interface.

Would this be possible ?
I presume this is not currently implemented but it should not be too complicated... The only problem I've found is with the reminders. Currently, the reminders are executed by the clients (WebService, iCal, Outlook ... ) when they update their info and a meeting is close, is this correct ? Or are there some Java Listener Interfaces that would be invoked on reminder events ?