I'm assuming you're wanting to do this for a single mailbox. If you're using Exchange on the backside (as opposed to Domino), it is possible. Might be possible with Domino, but I don't know.
You will need to use a utility like the Exmerge utility directly with the exchange data store. You can google it up fairly quickly. A couple of good links I found that might be useful are below:
http://support.microsoft.com/kb/174197
http://www.petri.co.il/brick_level_backup_of_mailboxes_by_using_exmerge.htm
Cliff
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