In our default class of service, we have E-Mail message lifetime set to 90 days. Unfortunately, we're not quite 90 days into our installation, so I can't say for sure what happens at that point, but it appears that users have access to "Edit Properties" on any folder, which they can choose from four retention and four disposal policies we've defined, plus "custom", which seems to let them have their complete say in message lifetime. How can we remove custom, so no one can exceed our defined policy?

We're on Zimbra 8, 64-bit Ubuntu.