So I've successfully forwarded mail from my postfix server to remote Gmail accounts using /etc/aliases and newaliases. But now of course those Gmail accounts cannot send email originating from the original, aliased addresses without further configuration. I examined the Gmail configuration and found that it is indeed possible to forward sent emails via SMTP through the postfix server, but an account with a password is necessary.

Even though those accounts are simply aliases, is it possible to give them passwords to facilitate replying to emails they forward? Or is an entirely different configuration set-up necessary?