I recently setup an Exchange 2010 in an Exchange 2007 environment. All user (minus test accounts) reside on old 2007 server. OWA and mx record both point to new 2010 server. THis worked great for about 3 weeks. Now every other day, we are unable to receive external email. Once I reboot new Exchange 2010 server, mail flow works fine....for a couple days. Then it stops again. I cannot find anything in the event logs. Any ideas?