I have a customer whose emails to me are being returned as undeliverable.?

he asked me to ask my IP person to release mail from @soufun.com because his messages are not getting to me. He is getting this message: "Hi. This is the deliver program (remote) at soufun.com. I'm afraid I wasn't able to deliver your message to the following address. This is a permanent error; I've given up. Sorry it didn't work out." He is trying to send emails to my yahoo account. How do I correct this as his messages are very important to my business? Thanks.