Outlook sent item internet header missing

I have written a C++ app that sync's Outlook emails with our central server DB. Incoming messages contain MessageID info in the internet header - I use this for key generation 开发者_运维技巧when placing the messages in the central DB. However, Sent Items in Outlook do not seem to have Internet Headers, so I am stuck for a static id I can use to generate a unique, static GUID for placing the message in the central DB. Multiple Outlook stores are being scanned for multiple users, each user running a copy of the sync program. To be clear, if Pete sends an email to Joe, the email in Pete's Sent Items folder needs the same id to be generated as the id generated for the email when it arrives in Joes Inbox folder - Pete & Joe are both running the sync software.

Does anyone know whether: 1. You can grab a static MessageID from a Sent Items email item 2. If not, is there another value within the Sent Items email that will be available to the sync app scanning the Sent Items folder, and available to the sync app scanning the Inbox that the email eventually arrives in.

Users could be running Outlook 2002 upwards.

Thanks very much.

The MAPI property PR_INTERNET_MESSAGE_ID is set for outgoing and incoming items.