Reading and changing OWA Settings
In OWA 2003, there were OWA settings mirrored in properties on the root folder of mailboxes which WebDAV could get to. There was limited support for accessing a few of these properties with WebDAV. The online docs still state that these properties are there, however this is not really true for OWA 2007. You will see these properties on mailboxes which were accessed under OWA 2003, however they only work under 2003. If a mailbox is moved from Exchange 2003 to 2007, you will see the properties set still, however they are not used or maintained by OWA 2007. OWA 2007 stores many of its settings in hidden items in the users mailbox. There is NO support for accessing any OWA settings stored in these hidden items and you really should not write code against these items.
I’ve seen many requests for accessing this information. The next version of Exchange/OWA may store the OWA settings in a different place and any application written to access those hidden items may break in the next version of Exchange. Further, any programs changing the contents of these hidden items may break OWA.
The product team is keenly aware of the need for an API to access these settings, however there is nothing supported for accessing OWA 2007 settings and very, very little support in accessing a few properties with WebDAV in OWA 2003. Note that some of these settings which were supported with WebDAV against Exchange 2003 are covered with Exchange Web Services (Exchange 2007).
Customers sometimes want to use the settings for OWA for their own application. The better way to go is to store their settings in a custom property or their own hidden item and maintain its setting with their own code.
Getting User Availability (Exchange Web Services)
Setting OOF Messages (Exchange Web Services)