MS Exchange can’t get mail

We have a very small network using MS Exchange 5.5 sp 2 to distribute mail for our domain. Everything was fine last week, then the power went out over the weekend. After reboot, everything was normal except that Exchange is now rejecting all mail toour domain. I have checked the configuration and can’t find anything out of place. our domain is listed in the routing tab of IMC as routed to . The server can be reached from the net and exchange answers. It just doesn’t seem to know our domain anymore. Any suggestions