enableMailboxManagement REST API

Hello Members,

I would like to enable the new mailbox management feature for a lot of administrators. There are over 1000 acls, I cannot do this with the gw admin console, because it has a limitation. It displays only the first 1000 acls, and there is no next page button. I have to do this with REST API. Unfortunately I cannot find the required parts in the documentation. The acl add and remove features are there, but there is nothing about the mailbox management checkbox. After some digging, I've found that the feature is managed by the "enableMailboxManagement" tag, which can be true or false. But how can I change it? I tried to obvious "update" command and it runs without an error, but also does nothing.
Do you know the correct syntax for this?

Gellert