There's a few ways I can think to do that, but they might take a while depending on how much data you have.
1) You could go to the BASIC>Reports page and do an Email Activity Report. Set the number of rows to something huge. That will give you a report of who has sent how many items, and you could get the data from there.
2) You could go to the search page and run a search for something that grabs all mail, like a Date search for everything after 1970. Then use the "Export to CSV" under the Tools button to get a CSV file of information on every email in the system. You could parse that for what you need. This could take a LONG time to export.
Hope that helps, feel free to call into support if you want to talk to someone in person about it.
Barracuda Message Archiver