Best way to delete an user mailbox with mdbox format and all attachments detach/dedup ?

[Tan]

        Hello everybody,

   On a Dovecot 2.x, what is the best way to delete an user mailbox when : 
* all attachments for all users detach in a common directory (mail_attachment_dir = var/mail/attachments ).
* attachments use SIS deduplication (mail_attachment_fs = sis posix)
* mailbox are in mdbox 

Trying to delete user mailbox directory (rm) and do the command  : doveadm -v purge -u johndoe , all attachments of this user are orphelins.
In another way, is there a dovecot command to delete or to synchronize attachments ?

Best regards,
TaN