First thing first, using the manual, your commands will go in dry run mode, no hints are given on why needed changes are counted but not executed, this is because you have to rn the command with the y switch to do the changes, here are a few ones you will use often
dbmail-util -dy – set delete status on deleted mail (deleted by IMAP or POP)
dbmail-util -py – delete messages with delete status
dbmail-util -by – rebuild the caches
Without the Y, no changes will be made to the database