I have recently had my ISP update their nameserver so that reverse proxy will resolve to the mailserver. However, after the change I cannot seem to be able to send emails outside. All the emails are sitting on the deferred Queue with "Delivery temporary suspended". I have tried postqueue -f without any success and checked without anti spam/ virus - but it's the same. Anti spam/ Anti virus / Permissions are looking good.

Any suggestions on how I can resolve this? I can seem to be able to receive emails fine..