In VPOP3 versions 3 and later, VPOP3 uses an external Database (PostgreSQL) for storing data, such as message data, logging, configuration details etc. Because of the importance of this information, it is strongly recommended that this data is backed up regularly.
By default, every day VPOP3 will backup the database to the VPOP3 installation directory as a file called 'DBBACK-x.DMP', where 'x' is the day number (0=Sunday, 1=Monday, etc). This means that the backups cycle on a weekly basis, so they don't grow indefinitely, and you always have a few backups even in case the latest one fails.