I know the way to disable all local delivery is to remove the domain from "mydestination", which will cause all mail to be relayed through whatever relay I setup. But I want postfix to accept all mail from GApps for local delivery to dovecot, but relay all locally generated mail back to GApps.
Ex: I have webmail running on the server, using the local postfix. email@example.com sends an email to firstname.lastname@example.org. If the user2 exists locally postfix delivers locally, doesnt exist - I could add an fallback relay which would send that mail to GApps. But I want postfix to always relay these mail back to GApps (which will send these mails downstream back to postfix for local delivey) regardless of local availability. So that I can have a kind of waterfall model.
I know there are a lot of related questions to this (none of the answer this specifically), but basically what I want is to have a kind of identical inboxes for same users at both the gmail and local dovecot. I have found a temporary fix by directly using GApps SMTP Relay instead of local for the webmail, but that doesn't solve anything for those connecting with IMAP (would end up having to give each user access to GApps SMTP).