Are you referring to Mail authentication via domain owner password?
Right now, the closest thing to what the original poster wants, at least as I understand it, is by default, symlinks are created from the account's default address to the mailboxes that are created. That allows the cPanel account user to log into the default mail account using Horde and read the mailboxes on that account. Note that this only works with Horde, and only works if the symlinks exist - they can be deleted without breaking anything.
The Tweak Setting I mentioned will allow mail authentication using the domain owner's password, but the user would need to log into each account individually. The symlinks that allow Horde to view all mailboxes in an account from the default mailbox is, in my opinion, a more elegant approach, but it only works for Horde.
