Sounds like you have secured the Outgoing email so much to prevent relay that you have now disabled all email. Check your relay settings.
Also, check your mail transport settings and also make sure DNS resolution is working on the server as this will prevent email from being sent. The easiest way to test this is in a DOS window using PING to various Domain names from the server.
Also, as an outside possibility you might be an open relay and be activity blocked from sending emails. There are various web sites you can check for Open Relay.