Well, this is the thing. Purely in an amateur, user sort of way. ( I'm sure these things are discussed in Comp Sci courses) it seems to me that data should be stored in a database. But documents should be stored in folders. Which to me would suggest that an email programme's database should be there to index the emails; but the emails should be in a folder. If the database falls over the emails, or at least a backup folder of the emails, would still be there.