I am running exchange 2013, with CU3. Everything seems to be running fine, but Google is trying to send us emails.
It's for google hangouts.
What's interesting is that we're receiving emails just fine from email@example.com, but when they send us other emails for google hangout, it doesn't work. They are claiming they are receiving the below error message.
Description: Google tried to deliver your message, but it was rejected by the server for the recipient domain domain.org by mail.domain.org. [66.xxx.xxx.xxx]. The error that the other server returned was: 550 Administrative prohibition
I've done some googling, but nothing concrete comes up.