Hello IT Pros! I have just migrated from exchange 2003 to exchange 2007; all was going swimmingly until I started receiving messages undeliverable messages such as this one bay0-mc11-f14.bay0.hotmail.com #550 DY-001 Mail rejected by Windows Live Hotmail for policy reasons. We generally do not accept email from dynamic IP's as they are not typically used to deliver unauthenticated SMTP e-mail to an Internet mail server. I have received similar emails from other providers (this one was from trying to send to a Live hotmail address) that say similar stuff about unauthenticated SMTP mail. It is true my IP is dynamic, however it only changes about twice a year and it was all working fine before migration. I have a feeling its got something to do with DNS, although I may be wrong Any help would be fantastic! Kris

Simply put your ISP has submitted a block of IPs that are Dynamic to prevent bulk mailing and of course it forces companies to pay up for the dedicated IPs. Only they can request the removal.