All MAPI interfaces are OLE COM interfaces that use RPC services for marshaling data across process boundaries. If the Remote Procedure Call Service returns an error, a corresponding MAPI error (as shown in the following table) is returned to the calling application. For more information on OLE custom interfaces, see the Platform SDK.
RPC-Related MAPI Error Codes
| RPC Error | MAPI Error Returned |
|---|---|
| RPC_S_ACCESS_DENIED | MAPI_E_NO_ACCESS |
| RPC_S_NOT_LISTENING | MAPI_E_SESSION_LIMIT |
| RPC_S_SERVER_UNAVAILABLE | MAPI_E_NETWORK_ERROR |
| RPC_S_OUT_OF_RESOURCES | MAPI_E_NOT_ENOUGH_MEMORY |
| RPC_S_SERVER_TOO_BUSY | MAPI_E_CALL_FAILED |
Because the Microsoft Exchange Server information store provider automatically retries calls that return these RPC errors, you need not do so in your own code. This process differs from that in use by the directory service; for more information, see Network and RPC Error Codes for Directory Operations.