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Initializes a transport provider for operation.
A transport provider must implement XPProviderInit as an entry point function in the provider's DLL. The implementation must be based on the XPPROVIDERINIT function prototype, also specified in Mapispi.h. MAPI defines XPPROVIDERINIT to use the standard MAPI initialization call type, STDMAPIINITCALLTYPE, which causes XPProviderInit to follow the CDECL calling convention. An advantage of CDECL is that calls can be attempted even if the number of calling parameters does not match the number of defined parameters.
A provider can be initialized multiple times as a result of appearing in several profiles in simultaneous use or of appearing more than once in the same profile. Because the provider object contains context, XPProviderInit must return a different provider object in lppXPProvider for each initialization, even for multiple initializations in the same process.
The transport provider should use the functions pointed to by lpAllocateBuffer, lpAllocateMore, and lpFreeBuffer for most memory allocation and deallocation. In particular, the provider must use these functions to allocate memory for use by client applications when calling object interfaces such as IMAPIProp::GetProps and IMAPITable::QueryRows. If the provider also expects to use the OLE memory allocator, it should call the IUnknown::AddRef method of the allocator object pointed to by the lpMalloc parameter.
For more information about writing XPProviderInit, see Initializing the Transport Provider. For more information about entry point functions, see Implementing a Service Provider Entry Point Function.