I have a user that is having some issues with an incoming email from an one outside customer. If the customer creates a new email to my user, it bounces back saying "The following organization rejected your message: mail.MyExchangeServer.com". If the customer replies to a existing email thread, the email will be delivered fine to my users. I have tested new outside emails to my user from google, yahoo, etc and new email are delivered fine. It seems to be isolated to this once customer. I haven't had any other issues or reports of bounce back from any of my other users/customers. I had the custome try to type in the full email address of my user, not using auto file, but no change. I had the customer email me, same issues. I have check and neither of us are on any type of blacklist. I checked my spam server and its not even showing the bounce back email hitting it.
Any thoughts, is the issues on my email server or the customer's email server or somewhere else? THX - John