When someone emails us from a certain domain, the email is lost. All the other domain's work but not this one. It doesn't show up in the inbox or even the junk mail folder. I have to specifically white list each email address for that domain. Even when I disable all the spam detectors in exchange, it still doesn't recieve. Why is this?

have you got message tracking enabled? could you track the message and post the results? also have you got any smtp hosts touching mail before it hits exchange?

There is a postfix mail relay that touches the mail before passing it onto the Exchange server. When i send a message I immediately get a message back saying: Your message did not reach some or all of the intended recipients. Subject: 12:19 Sent: 8/12/2008 12:19 PM The following recipient(s) could not be reached: 'kalebh@mydomain.com' 8/12/2008 12:19 PM 550 5.7.1 <kalebh@mydomain.com>... Relaying denied The main reason why I think it is the Exchange server is because when I whitelist the specific emails, it works fine.

Clarify: users cant get mails from a specific external domain, right? Troubleshooting: 1. Use message tracking to see if messages are unable to get to exchange server 2. The NDR is from sender, right? Can you post the detailed internet header of it for analysis? And also provide related environment info about the internet header in the NDR Collect info: 1. Where do you set the whitelist? 2. Which version of exchange do you use, 2003 or 2007? Do you use Edge if its Exchange 2007?