[exim] Route replies to "shared" mails back to other recipie…

Hi.

Suppose i have a single "shared" mailbox, which redirects mail to several other user's mailboxes (so, several users read incoming mails). And then one user replies. But other users won't see this reply. How can i route reply to other users too (well, "other users" means only users to whom initial mailbox was aliased)?

I'm thinking about identifying original message recipient (i.e. "shared" mailbox) using Message-ID header, and then looking up its aliases, but it seems Message-ID does not contain localpart, only domain.

This seems similar to maillist, but is there a way to implement this without special maillist software?
Using exim only? Or maybe exim and imap/pop3 server (i'm using dovecot)?

Thanks.