Yes. Its like a giant excel spreadsheet that holds message properties.
There is a "Messages" table in the database that takes up the bulk of the
database size. Some of the properties include the subjects, authors, dates,
size, messageIds, etc. Many of these are what you see displayed in the
message list columns. That information is in the database so you don't have
to load up each message each time you display the list of messages for the
folders.
The database is also responsible for keeping track of newsgroups and their
lists and the subscriptions.
It also stores the information on what messages have been downloaded from
what accounts.
steve