I have a mailbox that I can send to from my Outlook client, but when I send to the same address via any other method, it often, but not always, sends an NDR. The AD object has what appears to be 2 good SMTP addresses and a valid X400 address. If I send from Gmail (for example) I get this error message: 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. <bux2k.binghamton.edu #5.1.1> This does not happen every time.