Register your server (the one sending email) with SenderID http://www.microsoft.com/mscorp/safety/technologies/senderid/overview.mspx http://www.microsoft.com/m

Register your server (the one sending email) with SenderID http://www.microsoft.com/mscorp/safety/technologies/senderid/overview.mspx http://www.microsoft.com/mscorp/safety/technologies/senderid/overview.mspx which is an MS invention -- their record wizard is here: http://www.microsoft.com/mscorp/safety/content/technologies/senderid/wizard/ http://www.microsoft.com/mscorp/safety/content/technologies/senderid/wizard/ The rest of the world (at least those email servers that check for this stuff) uses SPF records. This site http://www.openspf.org/ http://www.openspf.org/ tells you how to setup SPF on your server.