[Dovecot] How to manage Seen flags via sieve?

[Max Ivanov]

I use public namespace for group mailboxes. If someone sends email
from this mailbox , MTA detects it and delivers copy of that message
to mailbox/Sent folder, to keep history of all messages available for
every group member. I'd like to set Seen flag on all messages that
dovecots deliver puts into "Sent" folder. Is it posible somehow?