[Dovecot] Reporting NFS quotas via IMAP

I'm confident that the question has been asked before, but I can't
remember the answer.

I have -- dovecot 1.1.2 -- Mail storage (maildir format) on NFS -- Quotas on that file system -- A working rquotad -- mail_plugins = quota imap_quota in the protocol imap section -- quota=fs in the plugin section

I get (using Apple Mail as a client) -- Notification that the account supports quotas -- No information about the size of the quota nor the usage

I probably do something stupidly wrong. The WIKI tells me that fs
quota support RPC (i.e., rquotad), so I'd expect my client to report
the quota to me. Using quota(1) on the mail server works as expected.