Are you sure? I know that postfix can use the same backend databasefor authentication as dovecot, and dovecot can be the master, but dovecotdoes NOT listen on port 25 or 587 at all, those are all just used by Postfix.
Not true anymore. Dovecot added a submission service in a recent version. Dovecot can listen on 587, take the email, and pass it on to postfix to then go out to the world.
https://doc.dovecot.org/admin_manual/submission_server/
