What are Non Delivery Reports (NDR) and which servers generate these?

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Question

NDR’s are typically generated by one of two ways:

* By a remote server.
* By the same server.

There is a common misconception surrounding the way that NDR’s are generated and any possible “backscatter” produced as a result of returning a Non Delivery Report.

For example, administrators of GMS often use the incoming redirect feature to block all e-mail from a particular domain but are often concerned that GMS will create a vast number of NDR’s in the process. Is this the case?

Answer

No, this is not the case.

As your server issues a rejection and therefore does not accept the message, it should return a five (5) series error code which the sending server should interpret as a permanant failure. At this point, it is the responsibility of the remote sending server to generate the NDR back to the original sender, not GMS.

If your GMS server accepts the incoming e-mail message but later returns an error after the SMTP connection has been closed by both hosts, the generation of the NDR lies with GMS.
For example, if GMS accepts the message but for some reason is shortly afterwards unable to deliver the message to the users mailbox, it will generate an NDR.

Here is an external link to SMTP Enhanced Status Codes:

Keywords:ndr non delivery report backscatter

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