We've had many users request Beyond Compare add support to synchronize individual messages between copies of Microsoft Outlook. We have no plans to add this feature to Beyond Compare, instead we recommend using SynchPST.

Here's a description of SyncPST from the author:

'SynchPST for Outlook' is the ideal tool to synchronize your Outlook on a desktop and a laptop. You can sync your Outlook data files with each other or your Exchange mailbox with any other Outlook data file. The Professional Edition is able to synchronize your Outlook automatically.
Keep your Outlook data in sync while you are on the road!

Through the end of March 2009 we are running a cross promotion with Wisco, the maker of SyncPST. Use the coupon code "ZR3-GPC-L6D" to receive a 20% discount off the purchase price of either the Basic or Professional Edition of SynchPST.

You can also watch this month's newsletter from Wisco for a coupon good for a 20% discount on Beyond Compare licenses.