For some reason one of our clients is being blocked by our server. "houserwalker.com" Our domain is parrishconstruction.com. I have recently moved out MX record to a new domain getting rid of a 3rd party and using Exchange. I thought that this problem maybe a cashe issue on there end however they have rebooted their server and cleared the cash. Now they are sending through a third party themselves. What can I do on my end to allow their mail through?