This is the scenario:
I have a server with Postfix and some domains, and now, one of this domains want to use Gmail Google Apps only in a couple of accounts.
The end-user configure the domain with Google MX registrys, configure the mail accounts in Google and the other accounts points to my server.
I've configured the external accounts with transport to the MX.
When I send an email for example, from Hotmail, if the account is configured in Google Apps, google keep the mail, and if the account is in my server, then google transport the email to my server.
When internal accounts from my server send mails, I can decide what I do with it and transport to local account or to google.
The problem is:
When the accounts in Google Apps with my client domain try to send mails to same domain accounts, but in my server, my postfix reject this emails with the next message:
30 14:00:28 ***** postfix/smtpd: NOQUEUE: reject: RCPT from mail-la0-f43.google.com[18.104.22.168]: 553 5.7.1 <email@example.com>: Sender address rejected: not logged in; from=<firstname.lastname@example.org> to=<email@example.com> proto=ESMTP helo=<mail-la0-f43.google.com>
This is normal, but... how I can permit relay from google to this users/domain only?
I call to Google Apps support, and they say they don't permit smtp auth on my server to send this mails.