[Dovecot] Single instance storage

[Jean-Daniel Beaubien]

I have read most of the doc on the dovecot website, and couldn't find any
info on the single instance storage feature, so I'm posting my questions
here.

- Are these 3 parameters the only one necessary for single instance
storage? I cannot find any doc on this feature on the website; is there
anything specific I need to know about them? (the last one isn't exactly
self-explanatory).
- mail_attachment_dir = /srv/vmail/attachments
- mail_attachment_hash = %{sha256}
- mail_cache_min_mail_count = 2

- Is this feature ready for production?

Thanks,

-JD