Calendar Architecture

For the most part, Connector uses iCalendar for Exchange calendaring. Many iCalendar properties are also automatically promoted to WebDAV properties in the urn:schemas:calendar: namespace. In particular:

`DTEND`	`urn:schemas:calendar:dtend`, aka `E2K_PR_CALENDAR_DTEND`
`DTSTART`	`urn:schemas:calendar:dtstart`, aka `E2K_PR_CALENDAR_DTSTART`
`LAST-MODIFIED`	`urn:schemas:calendar:lastmodifiedtime`, aka `E2K_PR_CALENDAR_LAST_MODIFIED`
`UID`	`urn:schemas:calendar:uid`, aka `E2K_PR_CALENDAR_UID`

These (and others) can be used in searches to find specific events or ranges of events.

The iCalendar data can be found in either of two ways:

By doing a GET and parsing the iCalendar data out of the returned message body
By retrieving the object's PR_INTERNET_CONTENT property via a PROPFIND or BPROPFIND.

The second method only works on objects that were created as iCalendar objects (ie, created in Evolution). Objects created by Outlook will not have the PR_INTERNET_CONTENT property set, so we have to fall back to using GET. Also note that for some reason, PR_INTERNET_CONTENT will not be returned by the SEARCH command. Only by PROPFIND and BPROPFIND.

Exchange uses some non-standard iCalendar properties, and uses some properties in non-standard ways. Here are some of the things we know:

All-day events

Exchange does not use iCalendar DATEs, only DATE-TIMEs. To represent an all-day event, it sets the DTSTART and DTEND to UTC values corresponding to the boundaries of the day in the local time zone, and then sets the X-MICROSOFT-CDO-ALLDAYEVENT property to TRUE.

Free/Busy Transparency

Exchange allows an event to have any of four different free/busy status: FREE, TENTATIVE, BUSY, or OUTOFOFFICE. This information is kept in the X-MICROSOFT-CDO-BUSYSTATUS property.

Sometimes events created by Outlook or OWA will not have an iCalendar TRANSP property, so we must fake it based on the value of X-MICROSOFT-CDO-BUSYSTATUS.

Meeting requests sent from Outlook also have an X-MICROSOFT-CDO-INTENDEDSTATUS property. This seems to be used to indicate what BUSYSTATUS value the organizer intended the recipient to use.

Priority

X-MICROSOFT-CDO-IMPORTANCE essentially duplicates PRIORITY. It can be MAPI_IMPORTANCE_HIGH (0), MAPI_IMPORTANCE_NORMAL (1), or MAPI_IMPORTANCE_LOW (2).

Recurrences

An object in an Exchange calendar folder can be one of four different kinds of "instance":

A non-recurring event.
The master entry for a recurring appointment.
A single instance of a recurring appointment. These objects are generated when you view your calendar in OWA, but are redundant with the information in the appointment's master entry.
An exception to a recurring appointment. (It is not clear that these actually appear in WebDAV.)

The instance type of an object is stored in its X-MICROSOFT-CDO-INSTTYPE iCalendar property, which is also visible as the urn:schemas:calendar:instancetype (aka E2K_PR_CALENDAR_INSTANCE_TYPE) WebDAV property, with one of the values cdoSingle (0), cdoMaster (1), cdoInstance (2), or cdoException (3), corresponding to the four types described above.

Last Action Time

Outlook/Exchange keep track of the last time an action was taken with respect to a meeting request in the X-MICROSOFT-CDO-REPLYTIME property. When accepting a meeting request, it should be set in both the saved meeting and the reply to the organizer. It must also be set in a direct booked meeting. Outlook displays this timestamp to the user when viewing the meeting.