One of my co-workers attempted to send an e-mail to a customer yesterday. The mail was returned with the following error: "There was a SMTP communication problem with the recipient's email server. Please contact your system administrator. <ourservername #5.5.0 smtp;554 mail server permanently rejected message (#5.3.0)>
I have investigated RFC 3463 and it indicates vaguely that a "permanent failure" has occurred and that "some change to the message or the destination must be made for successful delivery". It also says that "Something was wrong with the protocol necessary to deliver the message to the next hop and the problem cannot be well expressed with any of the other provided detail codes".
Can anyone help clarify this for me? It seems like perhaps the message was considered spam and rejected? (from the 554 code). I'm rather confused. Any help would be greatly appreciated. Thank you!