dovecot - Aug 2021 - Enabling autoexpunge for mailboxes created by sieve rules

Hi everyone. I have global sieve rules that can create mailboxes
automatically by using "fileinto :create
some/mailbox/that/does/not/exist".
The emails are delivered to dovecot using lmtp and I can see the
mailboxes created just fine.
Is there a way to configure all new mailboxes created by those sieve
rules to automatically set to autoexpunge after 15 days ?

I tried this , but it did not work.

namespace {
  type = public
  separator = /
  prefix = mypublic/
  location = maildir:/var/spool/vmail/dovecot/mail/
  subscriptions = no
  list = children
  mailbox * {
    autoexpunge=15d
  }
}

plugin {
  acl = vfile
}

# dovecot --version
2.3.15 (0503334ab1)


Thanks!