Office 365 received the message that you specified. Unfortunately, we haven't been able to deliver it to the recipient ({0}) ...

Office 365 received the message that you specified. Unfortunately, we haven't been able to deliver it to the recipient ({0}) yet. We can't deliver the message because the service can't connect to your organization's email server (on-premises server). Your organization's firewall is blocking messages sent from Office 365 to port 25, or your server isn't running.