Hi, my name is Osvaldo and i'm having a problem with my exchange 2007 server. Someone in another domain is trying to send an email to our distribution list and she is getting the following error: Delivery has failed to these recipients or distribution lists: ditribuitionname@mydomain.xx.yy The recipients email address was not found in the recipient's email system. Microsoft exchange will not try to delivery this email for you. Please check the email address and try ressending this message, or provide the following diagnostic text to your system administrator. The following organization rejected your message: mail.mydomain.xx.yy ... But it only happens when the person try sending to a distribution list, when sending to an induvidual like me it works fine. Please help        

Have you verified the email address for the DL? 100% confirmed it's correct? The sender, are they external or part of the same Exch Org? Can they send from OWA and test, could be a wrong/corrupt cache.Sukh

Check the group to make sure it is not required that the user be authenticated for mail delivery to happen. You description sounds like it is an external user and they would receive an NDR if the group was never changed, the default setting is to require users to be authenticated in order to send mail to the group.

hi, All members in the Dl can't receive message or part of them? Have you do some change? Like move some members from the Dl. Use the message tracking log to track the message that sent to the DL. Find more information about your issue. hope can help you thanks,CastinLu TechNet Community Support