There is an update (KB950219), which extends Outlook 2007’s support for the iCalendar standards. The update also improves Outlook 2007’s compatibility with some IMAP e-mail servers.
This update adds support for the following iCalendar features:
- Propose New Time for iCalendar Meetings: Users can now respond to a meeting invitation received in iCalendar format with a proposal for a new meeting time.
- Extended Yearly Recurrence: Supports recurrence patterns for appointments or meetings that recur every N years, where N is greater than or equal to 1.
This update also includes miscellaneous improvements to IMAP compatibility.
You can download this from Microsoft Download Center.