The message store is a database persistence mechanism that has been designed to allow you to do audit-tracking. The message store reads and writes messages upon request. Each message must have a unique identification number. As with other ESB services, the message store is "pluggable", which means that you can "plug in" your own persistence mechanism should you desire to do so, though a default database persistence mechanism is supplied.
In the event of a system failure, the message store is also used as a holding place for messages that need to be re-delivered.
If something other than a database is required, such as a file persistence mechanism, you can write your own service and then override the default behaviour with a configuration change.