I have an Exchange server 2003 with sp2. I have one domain that I am trying to send an email too that I get a bounce back from my server of message 550 unrouteable address. I can receive emails from this person and have checked with my web hosting company that we relay our out going emails through to make sure we are not blacklisted. The provider can send mail to this domain in question and can receive as well. I have had the owner of the other domain check with their provider to make sure that nothing is getting blocked and to make sure the provider he is using does not have a problem with us relaying email through our web hosting company. There was nothing that came up on their end. The fact that I am getting this bounce back from my Exchange server lets me know that it is not even leaving my network. I am not having any problems sending mail to any other domains and receiving mail is working fine. I have been told that it may be in my DNS of the exchange server. That is may be holding an old DNS entry for the domain. Any help on this matter would be greatly appreciated. Thank you in advance.