The Public Folder–Based Free/Busy protocol allows information about the availability of a user or resource to be written to and read from a shared location so that it can be used to effectively and efficiently schedule meetings. This information, referred to as free/busy data, is specified in the properties of a free/busy message that is created in the public folders message store. The properties of this message are set to reflect the free/busy status and related details of the user's or resource's Calendar object. The free/busy status falls into four categories: free, busy, tentative, and Out of Office (OOF).
Free/busy data can also be obtained by using the Availability service, as described in [MS-OXWAVLS], and by directly accessing the calendar of another user or a resource and reading the free/busy status property, as described in [MS-OXOCAL].
This protocol extends the Message and Attachment Object Protocol, described in [MS-OXCMSG], in that it defines new properties on a Message object and adds constraints to the existing properties of a Message object.