archive disabled users
I created zero days policy, assigned it to new provisioning group, ranked #1, this provisioning group targets specific OU where disabled users are located.
set registry to ProcessHiddenMailboxes = 1 and ExcludeDisabledADAccounts = 0
I didn't set automatically enabled, on purpose, as we want to enable few mailboxes only at the beginning.
reset services, run provisioning group, the only mailboxes that apear in the "enable mailbox" wizard are the 7 mailboxes in that OU that are not hidden / disabled.