The IMAPISupport::NewUID method creates a new MAPIUID structure to be used as a unique identifier.
HRESULT NewUID(
LPMAPIUID lpMuid
);
The IMAPISupport::NewUID method is implemented for all support objects. Service providers and message services call NewUID whenever they need to generate a long-term unique identifier. A message store provider, for instance, might call NewUID to obtain a MAPIUID to place in the PR_SEARCH_KEY property of a newly created message.
Do not confuse the MAPIUID structure that you register at logon time with the MAPIUID structures that are created by NewUID. The MAPIUID structure that you register when you call IMAPISupport::SetProviderUID represents your address book or message store provider to MAPI and is used to distinguish entry identifiers created by different providers. This MAPIUID structure should be hard-coded, using the output of the utility UUIDGEN.EXE, and not obtained through a call to NewUID.