The possible root cause of this issue is that the Secure Email Gateway server is unable to connect to the Exchange server. This could be due to network issues, firewall settings, or authentication problems. If the Secure Email Gateway server cannot communicate with the Exchange server, it will not be able to deliver email to the newly enrolled devices. The previously enrolled devices may still be able to receive email because they have cached credentials or sessions with the Exchange server. The users who reported this issue are able to access their email through OWA on their computers because OWA does not rely on the Secure Email Gateway server.