We are running Microsoft Exchange 2010 on a 2008 R2 Server. We have made no changes recently to the server and suddenly we cannot send mail internally or receive mail internally and we cannot receive mail externally. The only function we can do is send mail externally. I have tried to restart our sonicwall firewall that holds our send receive rules. I have also restarted the server a few times as well as restart Microsoft Exchange Active Directory Topology Service that restarts all the Exchange Services. I have not gotten anywhere with these can anyone suggest anything else?