I have a client with office 365 small business premium. One of the users has his mail forwarding to his other business email (the account is for a side business of his).
Frequently lately he has been getting error messages like :
# < 5.7.1.smtp; 550 5.7.1, unable to relay.ROU1>#SMTP#. We aren't trying to relay, it is just a forward to another account. The receiving server is an Exchange 2010 STD.
Not every email is affected by this. Any clues what could be causing it?