Since upgrading my Internet Bridgeheads to Exchange 2007, I have been seeing some surprising things happen with non-delivery reports (NDR). We host a large number of external contacts in our AD so they can be included on Distribution groups. We have a list called clients@domain.com that has 200 external people on the list.If one of those 200 addresses becomes bad and email sent to the clients@domain.com generates a NDR message that gets sent to the 200 people on the list.Is there something that can be done to avoid this happening?I went through and disabled deliver reports for the list. But that seems to have created a different issue where emails sent via the list do not include the RETURN-PATH entry and get bounced as SPAM. I have read the other threads here about RETURN-PATH as <> related to not wanting delivery info for OOO messages, so I assume they are related.Any help is appreciated.

Hello Chuck,I would suggest you to read the below thread.DSN messages disapears if send as distribution group addresshttp://social.technet.microsoft.com/Forums/en-US/exchangesvradmin/thread/e33d508b-61c0-4af4-ba1b-685cbba53b96Arun Kumar | MCSE - 2K3 + Messaging | ITIL-F V3

Am I correct in reading the thread you mention? The NDR in Excahnge 2007 are by default sent to the entire group, this is by design, and in-line with the specifications of teh RFC. On my first question, does disabling the NDR for a group mean that all messages sent through the group will have the Return-Path sent to <>? If I send to a group, the copies of that message sent externally have a blank return-path, which can flag them as SPAM.

To be more to tbe point, can you confirm that the mechanism used to enable the "Do not send delivery reports" is to set the Return-Path to <> on all outbound messages? That appears to be what I am seeing. I am still unclear on why Exchange is sending the expandedmessages with the Sender as the Group as opposed to the composer of the email, but I think that is a different point.