One of our salespeople routinely receives e-mail messages from a certain customer, but cannot reply or send new messages to this address. We use Exchange 2003, and I see the messages he sends or replies to just sit in the queue until they eventually time out and a NDR is sent back. I have tried from my exchange work address and the same thing happens. However, I sent this customer a message via g-mail which he received no problem.
Any ideas? If the customer's junk filter is catching our messages, would they sit in our queue retrying until they time out?