is it possible to add a custom special use mailbox

[Marc]

> 
> Currently I am using this to try and catch everything in Sent.
> 
>   mailbox Sent {
>     special_use = \Sent
>     auto = create
>   }
>   mailbox "Sent Items" {
>     special_use = \Sent
>     auto = no
>   }
>   mailbox "Sent Messages" {
>     special_use = \Sent
>     auto = no
>   }
> 
> I would like to have something
> 
>   mailbox Test {
>     special_use = \Test
>     auto = create
>   }
>   mailbox "Test Items" {
>     special_use = \Test
>     auto = no
>   }
>   mailbox "testing" {
>     special_use = \Test
>     auto = no
>   }

Is this page[1] out dated? Because I am getting errors having this imap_capability set. 

special_use: Space-separated list of SPECIAL-USE flags to use for the mailbox. There are no validity checks, so you could specify anything you want in here, but it's not a good idea to use other than the standard ones specified in the RFC.

    NOTE: Due to a bug in Dovecot v2.2.30+ if special-use flags are used, SPECIAL-USE needs to be added to post-login CAPABILITY response as RFC 6154 mandates. You can do this with imap_capability = +SPECIAL-USE

[1]
https://wiki.dovecot.org/MailboxSettings