Auto create & subscribe folder from Userdb [Was: Users with extra mailbox: namespace/mailbox in userdb lookup?]

[MRob]

>> We have a need for some users to have an additional folder created and 
>> subscribed for them.
>> 
>> Is is possible to return an override for the default "namespace inbox" 
>> containing the needed mailbox definitions in the userdb lookup for 
>> such users? If so, how would the userdb lookup result be formatted? 
>> Presumably as
> 
> Yes, see here:
> 
> http://wiki2.dovecot.org/UserDatabase/ExtraFields
> 
> Each setting ist one "Extra Field"
> 
>> just one long string, but how would the setting be named given there 
>> can't be a space in it? Can I replace the space with an underscore, 
>> e.g.
>> 
>> userdb_namespace_inbox = '{ mailbox Drafts { auto=subscribe 
>> special_use = \Drafts } mailbox Trash { auto=subscribe special_use = 
>> \Trash } }'
> 
> sort of:
> 
> userdb_namespace/inbox/mailbox/Drafts/auto=subscribe
> 
> see also:
> 
> http://www.dovecot.org/list/dovecot/2016-February/103140.html

Unfortunately, I'm having trouble with this task.

Dovecot 2.2.27

Trying to have an "Important" folder get created and subscribed for only 
some users. When I put this into my dovecot config file it works as 
needed (other folders omitted for brevity):

namespace inbox {
  mailbox Trash {
   auto=subscribe
   special_use = \Trash
  }
  mailbox Important {
   auto=subscribe
  }
}

But I don't want to do it globally, so put it into the userdb lookup:

SELECT .... 'subscribe' AS 'namespace/inbox/mailbox/Important/auto' ... 
WHERE ...

I confirmed that the correct query is executing and I know it works 
because other userdb fields are populated correctly. But the folder does 
not get created. For passdb lookups:

SELECT .... 'subscribe' AS 
'userdb_namespace/inbox/mailbox/Important/auto' ... WHERE ...

I'd appreciate help/tips.