I had an account that was having a hard time sending email using web based interfaces like Yahoo. They spent some time with the isp and I think they ended up calling Microsoft when they got no satisfaction. It ended up being a blackhole router. This article explains the concept pretty well. http://www.microsoft.com/technet/community/columns/cableguy/cg0704.mspx The pain in the butt was that they had to edit each computer on the network that wanted to use web based email. Just fixing the server was not good enough. After that incident I have done that edit on a few servers. Most of my accounts send email through Exchange so I have not had to suffer doing those edits on workstations, just the server..
The article I have a hard time finding. http://support.microsoft.com/default.aspx?scid=kb;en-us;314825
Don’t forget to do you reverse dns entry to send email to AOL and others that use rdns for anti-spam. http://www.dnsstuff.com/info/revdns.htm Did I mention that www.dnsstuff.com is a great troubleshooting website. It even has a email blacklist testing link. You really don’t want to get blacklisted because some of the blacklisting services hold you hostage. No way to break free from their blacklist without a new public ip.