Q

No NDR generated when someone sends e-mail to an empty Distribution List

About a month ago, I found that if someone removes all the names in a Distribution List, and you set an e-mail

address to that DL, when e-mail are received they are simply flushed by Exchange -- no NDR, no warning to the administrator, no message to the sender, absolutely nothing!

I have talked to Microsoft engineers and the only answer I got was: "It is by design!" Wow, I wish I could dismiss my calls that easily! So my question is: Should there be some mechanism to at least warn the mail administrator, instead of it just flushing the mail?

Look forward to your opinion. Best regards.


The engineer was right -- it is by design; and it is compliant with RFC 2821 which covers SMTP. Where NDRs are concerned, RFC 2821 says, in relevant part:

"If an SMTP server has accepted the task of relaying the mail and later finds that the destination is incorrect or that the mail cannot be delivered for some other reason, then it MUST construct an ?undeliverable mail" notification message and send it to the originator of the undeliverable mail (as indicated by the reverse-path). Formats specified for non-delivery reports by other standards (see, for example, [24, 25]) SHOULD be used if possible.

This notification message must be from the SMTP server at the relay host or the host that first determines that delivery cannot be accomplished. Of course, SMTP servers MUST NOT send notification messages about problems transporting notification messages. One way to prevent loops in error reporting is to specify a null reverse-path in the MAIL command of a notification message. When such a message is transmitted the reverse-path MUST be set to null (see section 4.5.5 for additional discussion). A MAIL command with a null reverse-path appears as follows:

MAIL FROM:<>

In your example, Exchange does successfully deliver the message. A distribution list may not have any members, but it will still have its own SMTP address. Say you have a DL called Peeps. There is a recipient then called Peeps@Mydomain.com (that recipient is the Peeps DL). When you send a message to this DL, it is delivered to it successfully. The fact that the DL is empty is outside the scope of SMTP (e.g., RFC 2821). Because the mail is sent and received successfully, there's no reason or justification for an NDR (because no delivery failure occurred).

Having said that, if you want an NDR to be generated, replace the DLs valid SMTP address with an invalid address. When someone sends something to that list an NDR will be generated.


This was first published in May 2002

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