[Dovecot] Questions about single intance storage

Hello

We are using dovecot 2.0.16 with mdbox+zlib. We are now testing SiS (Single Instance Storage) and I have 5 questions:

1º Is possible to "dedup" existing mdboxes? 2º Are attachments compressed with zlib if mdboxes already use zlib? 3º I have plenty CPU to spare, should I use a low value of mail_attachment_min_size , like 16KB ? 4º Can I "undo" SiS if I have problems? 5º We use bacula to save indexes & mdboxes, and we recover mailboxes using doveadm import when a user "makes a fatal mistake" wiping all her Inbox. If we enable SiS I am not really sure how can we safely restore a user's INBOX if that user has SiS attachments.

Thank you for your (great) support.

Maria