If configured, Instant Messaging pop-up reminders follow this architectural flow:
The Instant Messaging JMS subscriber subscribes to Calendar Server events and notifications in the Event Notification Service (ENS).
Calendar Server publishes an event or task notification in text/xml or text/calendar format to ENS.
The Instant Messaging JMS subscriber receives the calendar event or task notification and then generates a message in text/calendar format.
The Instant Messaging server sends the message to the calendar owner, if the end user is online.
If the recipient is available, Instant Messenger generates an HTML pop-up reminder on the end user’s desktop based on the message.