Backing up mail store

Trying to backup mail stores so I can migrate from 10.4 server to 10.6 server.

mailbfr -b is failing with the following errors.

rsync: readdir("/var/spool/imap/."): Input/output error (5)

rsync error: some files could not be transferred (code 23) at /SourceCache/rsync/rsync-35.2/rsync/main.c(992) [sender=2.6.9]

store and database are set to default in server admin which is /var/imap and /var/spool/imap.

Mail service is up and running and all clients are getting mail. When I go into /var/spool/imap to manually copy the store out its empty.

Where is the mail store? Where is all this mail going??