• logdb.db - this contains historical logging information for reports. It can be configured/disabled on the Logging → Admin logs page in the 'Historical Logging' section.
• spamfilter.db - this contains statistical information for the Bayesian filter section of the VPOP3 spam filter
• msgids.db - this contains summary information on the last few days' worth of emails, for duplicate detection
• archive*.db - this contains index information for the message archive facility in VPOP3
• user_*.db - these contain mailbox index information for the individual users
• quarantine.db - this contains information about messages which ahave been quarantined by the VPOP3 content/spam filter.

Certain database files can be deleted if they are corrupt (while VPOP3 is stopped) without causing major problems. If any database is deleted, VPOP3 will automatically create a new (empty) one when it restarts. Below is information about deleting the databases. Note that we do not recommend deleting any of the databases in normal operation (otherwise VPOP3 would delete them for you, or they simply wouldn't be made).

• logdb.db - this can be deleted. You will lose historical logging information, but nothing else.
• msgids.db - this can be deleted. You may receive a few duplicate messages (depending on how your Internet connection is configured), but that will resolve after a few days.
• spamfilter.db - this can be deleted, but the spamfilter will be less effective for a while.
• archive.db - this should not be deleted. If you delete this file you will lose the facility to search or backup the messages which have already been archived.
• user_*.db - these should not be deleted. If they are deleted, you will not lose any messages, but you will lose any IMAP4/Webmail message flags (eg read, answered etc)
• quarantine.db - this should not be deleted. If you delete this file, VPOP3 will lose the facility to access or tidy up any messages which are in the VPOP3 quarantine.