Our office uses both office 365 and Google apps. We were on Google apps first, and decided to give office 365 a try. Some folks liked it, some did not, and want to revert back to Google apps for mail.
We currently have our MX records pointing to Google apps and a routing rule sends all messages received by our Google apps account to the office 365 mail server.
When I add a Google apps routing rule to take messages to users in a specific group (those that want to use Google apps mail), and route them normally (to Google apps mail) External domain user's messages are received correctly, however mail messages originating from office 365 are not routed through the MX record (to Google apps mail). Office 365 docs specify that this scenario requires that the domain be configured as an "Internal Relay Domain", and I've set this option in
Office 365 -> Exchange Admin -> Mail Flow -> Accepted Domains -- (Edit Domain, check Internal Relay Domain)
However mails sent from inside office 365 addressed to users with accounts in 0ffice 365 continued to appear in office 365 mailboxes, and are not routed to the mx mail server (Google apps), and thus are not appearing in Google apps mail mail boxes.
It appears that Office 365 doesn't route the mails if the address exists in office 365's exchange address book. These users need to keep there office 365 accounts for Lync, Share Point, etc access.
I want Office 365 to route sending messages, either for everyone, or just specific users (the ones on Google Apps) through either the domain mx record (which is Gmail) or explicitly through the Gmail mail server.
If Disabling the Exchange app in Office 365 for these accounts is possible, I don't know how to do it, but removing these accounts from Office 365 altogether is not a viable solution.