[Dovecot] maildir S= and W=

Hi.

Even new mails delivered by my MDA don't get the ,S= and ,W= fields set... (but when I "upload" a mail via IMAP to dovecot, they are set)

Is there some place in dovecot where I need to enable this? Or would it be the MDA that has to calculate and set this already when placing a file in ./new?

Thanks, Chris.