I have read all the discussion here and checked that the check box is cleared. What is puzzeling me is that everything was working and then we started getting this error 10 days ago with no changes being made. The one possibility is that the mail server was out of date for updates for over 10 months and I applied all the patches to it the weekend before this started. Does anyone know if there might have been a software patch that could have caused this or if there is an internal default that might have been reset causing this problem? Thanks, Dalton Williams IT Manager Children and Addults with Attention-Deficit/Hyperactivity Disorder

That NDR message usually mean that the DG/DL or a mailbox has authentication enabled. This mean only a user who can authenticate to the AD i.e. internal user can send to the mailbox. Are you talking about DG or a user mailbox?

Hi Dalton, Agree with Michael. The NDR message usually mean that the DG/DL or a mailbox has authentication enabled. How did you get the error? Could you please explain your problem in detail? Do you mean that you have cleared “Required that all senders are authenticated” ? Thanks, EvanPlease remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.