I have one DL with 600 users. All users are internal users except one. That external user is not able to send the mail to that DL. He is sending the mail individually. While sending the mail getting below NDR. He is able to receieve the mail perfectly. We have exchange 2007 #552 4.3.1 Session size exceeds fixed maximum session size ##rfc822

Hi, Using Exch Management Shell check whether the flag "RequireSenderAuthenticationEnabled" is set to true get-distributionGroup "GroupName" |FL RequireSenderAuthenticationEnabled if its true then make it false like this set-distributionGroup "GroupName" -RequireSenderAuthenticationEnabled $false and then check. Regards,Laeeq Qazi|Team Lead(Exchange + Sharepoint + BES + DynamicsCRM) www.HostingController.com

Hi Avinash, How about your question? Any updates? Do you mean the external user cannot send any mails to the DL, regardless of size? Frank Wang