Our ISP made us change IP addresses which we did and everything seems to be working except exchange started having issues to one domain name, comcast.net that system manager just says an smtp protocol error occurred when trying to deliver the mail outbound. The IP change has happened over 120 hours ago so the ISP's can't blame internet propagation now but neither can tell me that they see any issues. There are no exchange errors in the application log, only VSS shadow copy errors that I don't know why they started appearing. All other domains outbound are working fine. Neither ISP can see a block on our domain or new IP.