I have a single Exchange 2010 sp2 environment with 3 DB stores. I am trying to reduce the sizes by moving the mailboxes to a spare DB and then deleting the empty database. I cleaned up the users mailboxes to reduce the sizes and set the retention periods to 1 day each and waited several days before moving mailboxes. The databases are backing up fine and clearing logs files but when I move the mailboxes I noticed they were taking a long time, even though some were less than 100MB. When I checked the new database size it seems like the orginal mailbox size might be moving (1GB instead of 100MB). Exchange is showing the expected smaller mailbox sizes when I run get-mailbox statistics against the DB. So if I have 5 mailboxes 100MB each it is showing like 3GB instead of around 500MB, and no whitespace. I keep waiting thinking mailby the retention period is not expired yet but it is much longer than 1 day already. I am setting them both to 0 today to see if that works.

What am I missing to get the combined mailbox sizes to match the DB size minus whitespace?