The IABLogon::Logoff method initiates the logoff process.
See IABLogon : IUnknown.
HRESULT Logoff(
ULONG ulFlags
);
The logoff process is typically started when a client calls IMAPISession::Logoff to end a session. MAPI then calls each address book provider's IABLogon::Logoff method to start the logoff process.
IABLogon::Logoff:
For more information about the logoff process of address book providers, see Shutting Down a Service Provider.