Correlation between MAPI Property Tags and Attribute Names

Accessing directory objects via MAPI is different from using directory API. MS Exchange uses directory schema with huge amount (five hundred or so) of attributes defined. The "directory" concept is different from MAPI concept, and differences start at the very fundamental level - names. For example, Exchange Administrator displays attribute names, which may seem strange or unfamiliar to a MAPI developer. This often leads to confusion.

There exists a relationship between attribute names and MAPI property tags. Microsoft Exchange Server Programmer's Reference comes with a subsection named "Directory Schema Attributes" in its "Reference" section, where a lot of attributes are listed with their corresponding MAPI IDs. For example, for Obj-Dist-Name attribute MapiID is 0x803C. This corresponds to higher 16 bits in MAPI property tag - MAPI property ID. Thus, for any attribute name it is easy to determine MAPI property ID (if one exists) by just looking into appropriate reference section.

You may wonder why some attributes don't have MAPI IDs. An example would be the "Governs-ID" attribute. This attribute defines a specific relationship between directory schema objects. Directory schema does not define any physical objects (such as a mailbox, for example), but rather their hierarchy, or collection of types and how they are related to each other. It would, perhaps, be correct to say that MAPI was not designed to encapsulate schema definition. This is the reason why some directory attributes don't have associated MAPI IDs.

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