One of the things that hasn’t changed in all these years with Exchange is Non-Delivery Reports. An NDR is an email that is sent when a message you send fails to go out. Exchange has had a consistent set of NDR status codes since version 5, just adding some here or there with changing technology (e.g. routing connectors, smarthosts, etc). Exchange has a lot of NDR codes at this point. I keep a little list running in my collection of files I spotlight to find the answer to recurring questions (which happens to always be 42). When an email bounces in Exchange, these codes explain why without having to be…