> Is that speculation or do you know it will happen?

I had troubles a few years back with e-mail routing from GMail to mail servers for a domain that had previously Google Apps set up for it but was subsequently moved to another provider. They disappeared after deleting Google Apps.

Maybe it's not an issue any more, maybe it was just some weird caching problem, maybe disabled domains are handled differently but it wouldn't also surprise me if they had some system for handling what is essentially mail internal to GMail.

Exchange will ignore MX records and deliver directly to accounts that exist in AD. This is true for some other email systems as well like Mirapoint. I'm not sure about Gmail.

When I set set up my email account at google apps few years ago my MX records were messed up, so no mail could be delievered to my new google app address from outside gmail. However, my regular test gmail account was happily sending emails that were received on my apps account although MX records were messed.

Thinks might have changed in the meantime, but my guess is that Google still sends emails directly for accounts that it "knows" are hosted on gmail and apps and happily ignore MX records.