The IMAPISession::CompareEntryIDs method compares two entry identifiers that belong to a single service provider to determine whether they refer to the same object. MAPI extracts the MAPIUID portion from the entry identifiers to determine the service provider responsible for the objects and then calls its logon object's CompareEntryIDs method to perform the comparison.
The CompareEntryIDs method is useful because an object can have more than one valid entry identifier. This situation can occur, for example, after a new version of a service provider is installed.
If CompareEntryIDs returns an error, do not take any action based on the result of the comparison. Instead, take the most conservative approach possible. CompareEntryIDs might fail if, for example, one or both of the entry identifiers contain an invalid MAPIUID.