Filtering Items Using a Boolean Comparison
Boolean values are specified differently in a filter in Microsoft Jet syntax than in a filter in DAV Searching and Locating (DASL) syntax.
In Jet syntax, boolean operators such as True/False, Yes/No, On/Off, and so on, should be used as is and should not be converted to a string. For example, to create a filter to return unread items, you can use this filter:
criteria = "[UnRead] = True"
If you convert the boolean value to a comparison string by enclosing it in quotation marks, then a Jet filter using any non-empty comparison string and filtering on a boolean property will return items that have the property True. A Jet filter comparing an empty string with a boolean property will return items that have the property False.