In Outlook, recurring events can be created with no end date. Calendar Server accepts events with no end date internally, but creates only 60 occurrences by default. Also, free/busy information is only kept up to the number of occurrences kept in the Calendar Server. For example, if you create a daily recurring event at 10:00 am in Outlook and the Calendar Server only keeps up to 60 repeating events, on day 61 the event still appear on Outlook but the 10:00 am time appears as “free” when calculating availability.
The default can be changed to a greater value by editing the calstore.recurrence.bound parameter in the ics.conf file. See Configuring Calendar Server in Sun Java System Calendar Server 6 2005Q4 Administration Guide for information about this parameter.