I'm making a research for our company in order to find the best way to upgrade our existing mail server (currently we are running open-source one). Since our managers have requirements to the new mail server, I've to ask those things before making offers to my superiors. As far as i read through the entire site, Zimbra offers anything that we'll need except one thing which is really important for us. We have (let's say) X managers, everyone of them have Y employees. The managers will need to (read-only without the possibility to delete/move/edit) their employees's mailboxes. And the CEO needs to have again read-only access to all manager and employees's malboxes. If this is possible to make Zimbra, it'll solve the most big issue with our research regarding our new mail server.
Your response and cooperation regarding this will be much appreciated!
Thanks for your time in advance.