zmmailbox -z -m
theshare@domain.com modifyFolderGrant /Folder account
user@domain.com rwix
You could do any of the following [account <name> | group <name> | domain <name> | all | public | guest <email> <password> | key <email> <accesskey>] followed by the permissions like r, rw, rwix, rwixd, rwixda, none, etc. (Where 'all' means everyone internal to your Zimbra box.)
(r)ead - search, view overviews and items
(w)rite - edit drafts/contacts/notes, set flags
(i)nsert - copy/add to directory, create subfolders action
(x) - workflow actions, like accepting appointments
(d)elete - delete items and subfolders, set \Deleted flag
(a)dminister - delegate admin and change permissions
The createMountpoint command is commonly used after this: zmmailbox z -m
user@domain.com createMountpoint --view appointment "/Vacation Calendar"
vacationcal@domain.com /VacationDates
(There are many ways to accomplish the same thing/can use more direct soap, or the utility built to simplify it, zmsoap. Or the web UI 'link to shared folder' to mount.)
Vote-
For exposing in web client:
Bug 15205 - share roles - custom (editor / author) levels
Specifically aimed at calendar timeslots:
Bug 12654 - Request Editor share level between Viewer and Manager
For ZCO:
Bug 35150 - RFE: Ability of customizing delegate Permission Level while sharing