As a retail business we get a lot of emails from customers using free Yahoo/Gmail type of accounts. Unfortunately the SMTP servers of these companies frequently find themselves being added to DNS blacklists for short periods of time. When this happens and a customer emails us, they get an NDR back from their ISP wich reads 'Mailbox Unavailable' or something to that effect. I realise that this NDR does not originate from your servers, but is there any way that the sender could get a more meaningful NDR?
Thank you for the suggestion.
I have forwarded this to the Product Development team and I will keep you posted.