Mailsmith does use a propritary database, but it is not one huge database like Entourage uses, each mailbox is a separate database. And the latest version of Mailsmith does not require backing up the whole mail package; the modified date of each mailbox is only changed if the mailbox changes. So backups should be much smaller now. And on top of that, the database is MUCH more stable than previous versions. Overall, I am very pleased with the speed and stability of mail storage in Mailsmith.