We have a customer who is having problems getting an email through to us. We have a Exchange 2003 Server which is running on Server 2003 box both are fully service packed. We run GFI MailEssentials for our Spam filtering to which I have whitelisted the customers domian name and sending mail servers IP address's. We are only having problems with this one new customer who keeps having mail bounced back to them with a 4.4.2 error as per below which is the error message they have sent to us via an alternative email address.
"Message delivery completed to the 212.35.253.xxx host with encryption setting of TLS based opportunistic TLS for recipient "email@example.com". The 212.35.253.xxx destination host returned delivery information of 442 lost connection with "my.emailserver" 212.35.253.xxx while sending mail from anddelivery status delayed."
There mail is being relayed via Websense-Email-Security-Gateway.
They believe the fault lies with our server but I can't get to the bottom of what is causing this problem.... help please!