Microsoft Exchange Server

Exchange Origin

Sample Contact Origin Filters

Query strings in the EWS Managed API and EWS are interpreted as a subset of AQS syntax. AQS strings are composed of either values or keyword/value pairs, separated by a colon (:).

keyword:value

When a value is specified without a keyword, all indexed properties are searched for the value. If a keyword is paired with a value, the keyword specifies a property to search for the corresponding value. See: https://msdn.microsoft.com/en-us/library/office/dn579420(v=exchg.150).aspx

I'm not sure if this criteria is the same for other Exchange folders or not.