We have just inherited a customer who have a Front-End and Back-End exchange configuration. Intermittently senders receive a bounce back from the Front-End server with the error 503 5.5.2 Send hello first.
Mail delivered to this customer goes through a 3rd party who run a smarthost service in a ‘filter and forward’ setup.
As this is an intermittent problem we are not sure where to start looking.
Any help would be much appreciated.