The MAPI spooler uses the IXPLogon::FlushQueues method to download and upload any pending messages to and from a transport provider. Typically, the MAPI spooler will flush the queues for all transport providers that are logged on to the session, starting with the first transport provider as set in the transport order section of the user's profile. Flushing queues is almost always the result of a direct request by the user, so the sending and receiving of messages while queues are flushing is synchronous to the MAPI spooler. Because these calls are synchronous, the transport provider should process them as quickly as possible.
Transport providers must handle the FlushQueues call as described in the following sequence of steps to enable proper message processing and to enable external resources such as modems to be used by other transport providers as part of the MAPI spooler's FlushQueues operation.
| Step | Component | Implementation |
|---|---|---|
| 1. | MAPI spooler | Calls the IXPLogon::FlushQueues method for the first transport provider listed in the transport order of the user's profile, passing the requested flags in the ulFlags parameter. FlushQueues is called once with all flags set for the entire upload and download operation. |
| 2. | Transport Provider | Needs to do a number of things before returning from the FlushQueues call. If previously submitted messages are being deferred, the IMAPISupport::SpoolerNotify method should be called with the NOTIFY_SENT_DEFERRED flag set. Note that it is possible for the MAPI spooler to cancel a message that has been deferred before the transport provider has a chance to finish processing the message. If the transport provider uses an external resource such as a modem, the connection to the external resource should be established. The STATUS_OUTBOUND_FLUSH bit in the PR_STATUS_CODE property of the transport provider's status row must be set using the IMAPISupport::ModifyStatusRow method. The transport provider should then return S_OK for the FlushQueues call. |
| 3. | MAPI spooler | Checks the transport provider's status row for the STATUS_OUTBOUND_FLUSH bit and calls IXPLogon::SubmitMessage for the first message in the queue. |
| 4. | Transport provider | Handles the message and returns from the SubmitMessage call. |
| 5. | MAPI spooler | If the transport provider returns S_OK from SubmitMessage, the MAPI spooler calls IXPLogon::EndMessage for the message as it does with regular message sending. If the transport provider returns a value other than S_OK from SubmitMessage, the MAPI spooler handles the value appropriately before calling EndMessage, or before calling SubmitMessage again. |
| 6. | Transport provider | Returns from EndMessage with its message processing status in the lpulFlags parameter. |
| 7. | MAPI spooler and transport provider | The SubmitMessage-EndMessage loop continues until all messages in the queue have been downloaded. |
| 8. | MAPI spooler | Notifies the transport provider that it has finished downloading messages by calling the transport provider's IXPLogon::TransportNotify method with the NOTIFY_END_OUTBOUND_FLUSH flag set. |
| 9. | Transport provider | Frees any external resources used in sending outbound messages so they can be used by other transport providers to flush their queues. The STATUS_INBOUND_FLUSH bit in the PR_STATUS_CODE property of the transport provider's status row must be set using ModifyStatusRow. |
| 10. | MAPI spooler | Checks the transport provider's status row for the STATUS_INBOUND_FLUSH bit and calls IXPLogon::StartMessage if it is set. |
| 11. | Transport provider | Processes the message and returns from StartMessage. If the transport provider has other messages to upload, it should call SpoolerNotify with the NOTIFY_NEWMAIL flag set. If the transport provider has no messages to upload, it should call IMAPIProp::SaveChanges on the message the MAPI spooler passed in StartMessage and return. |
| 12. | MAPI spooler | Continues calling StartMessage until SaveChanges is called on a message. After the transport provider has finished uploading, the MAPI spooler calls TransportNotify with the NOTIFY_END_INBOUND_FLUSH flag set. |
| 13. | Transport provider | Clears the STATUS_INBOUND_FLUSH bit in the PR_STATUS_CODE property of its status row using ModifyStatusRow and releases all external resources that have been released so they are available for use by other transport providers. |
| 14. | MAPI spooler | Calls FlushQueues for the next transport provider listed in the transport order of the user's profile. |
If a client application calls IMAPIStatus::FlushQueues on a transport provider's status object, the transport provider should set the appropriate bit in its status row with ModifyStatusRow. The MAPI spooler then calls the provider's IXPLogon::FlushQueues method at the MAPI spooler's convenience. When the provider's IXPLogon::FlushQueues method is called as a result of a client application's IMAPIStatus::FlushQueues call, the operation occurs asynchronously to the client application. Otherwise IXPLogon::FlushQueues works synchronously with the MAPI spooler.
For performance reasons, the MAPI spooler will only call a transport provider's FlushQueues method if the STATUS_INBOUND_FLUSH and STATUS_OUTBOUND_FLUSH flags are set in the transport provider's status row. Consequently, a transport provider can stop the FlushQueues operation at any time by clearing the STATUS_OUTBOUND_FLUSH and STATUS_INBOUND_FLUSH flags in its status row. If the MAPI spooler is shutting down and needs to end the FlushQueues operation, it calls TransportNotify with both the NOTIFY_END_INBOUND_FLUSH and NOTIFY_END_OUTBOUND_FLUSH flags set. The transport provider should release all external resources and return.