Glen's Exchange and Office 365 Dev Blog

The Categories or Keywords properties on a Mailbox Item is one of the more commonly used Item properties in Exchange. When you want to search for Items with a particular Category set it does present some challenges in EWS. With EWS you have 3 different search methods, the first being Restrictions (or SearchFilter's if your using the Managed API) that work like MAPI restrictions although you can't build restriction that are 100% equivalent to what you can in MAPI. One particular case is with the Categories property, because this is a Multi-Valued property (or String Array) the IsEqual and Contains Restrictions wont work like the Sproperty restriction in MAPI  http://msdn.microsoft.com/en-us/library/office/cc815385(v=office.15).aspx So the next type of Search you can do is a Search of a Mailbox folder using an AQS querystring which essentially does an Index search. Because the Categories property is an Indexed property this will work fine for Categories. The thrid type of Sea...