I have an Exchange 2003 server. One of my users has suddenly been generating NDRs when other people inside the network try emailing him. It is not always consistent, but it is happening somewhat frequently. The NDR is "The e-mail account does not exist at the organization this message was sent to. Check the e-mail address, or contact the recipient directly to find out the correct address." Now he is receiving these mails, but the senders are getting this NDR sometimes anyway. This happens for people both inside and outside our domain. Does anyone have any hints as to handling it?