I'm sure this is a simple matter, but MSDN and Google searches haven't yielded an answer. We started up an Exchange server to replace amail server utilizing a smaller company's mail server software. Yesterday we were able to send messages to a group, but today messages to the group are bouncing and the Exchange System Manager will not show us any users that we can add to the group to attempt to repair it. Emails to individual mailboxes are getting through OK. The File Server/ Domain Controllerwas rebooted at the close of business yesterday. What could cause this and how can we fix it?