Sending Messages using Hook Providers and Preprocessors

The following diagram illustrates the interaction between MAPI components involved in the message sending process.

The steps in this process are:

1. The message store provider, on behalf of a client application, notifies the MAPI spooler that there is a new message to send.
2. The MAPI spooler calls each registered preprocessor to act on the message.
3. The MAPI spooler delivers the message to any transport providers required.
4. Transport providers transmit the message to the underlying messaging systems.
5. The MAPI spooler calls each preprocessor's RemovePreprocessInfo function.
6. The MAPI spooler calls hook providers after all transport providers have completed their work.