I am upgrading from Exchange 2003 to Echange 2010 server (2008R2). They currently co-exist untill I move mail boxes and public folders to the 2010 server. I have moved a couple mail boxes from 2003 to 2010 and created a new mail box on the 2010 server. For those users they can send and receive mail internally and receive mail from external BUT can not send mail external. Any suggestions what I should look for?